8-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

The Securities Exchange Act of 1934

Date of report: December 21, 2006

(Date of earliest event reported)

US ONCOLOGY HOLDINGS, INC.

US ONCOLOGY, INC.

(Exact name of registrant as specified in its charter)

Delaware Delaware		20-0873619 84-1213501
(State or other jurisdiction of incorporation or organization)	(Commission File Number)	(I.R.S. Employer Identification No.)

16825 Northchase Drive, Suite 1300

Houston, Texas 77060

(Address of Principal Executive Offices, Zip Code)

(832) 601-8766

(Registrant’s telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrants under any of the following provisions:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under Exchange Act (17 CFR 240-14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240-14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

ITEM 1.01 ENTRY INTO A MATERIAL DEFINITIVE AGREEMENT

On December 21, 2006, US Oncology Holdings, Inc. (“Holdings”) entered into a Stock Purchase Agreement with Morgan Stanley Strategic Investments, Inc. (“Morgan Stanley”) pursuant to which Morgan Stanley acquired approximately 21.65 million shares of common stock and 1.95 million shares of participating preferred stock of Holdings for an aggregate purchase price equal to $150.0 million in cash. A press release announcing the foregoing investment is attached hereto as Exhibit 99.1.

On the same day, in connection with the consummation of the foregoing investment, Holdings, together with certain of its stockholders, including Welsh, Carson, Anderson & Stowe IX, L.P. , and Morgan Stanley entered into certain agreements, including an Amended and Restated Stockholders Agreement and an Amended and Restated Registration Rights Agreement, providing for agreements among such stockholders and Holdings with respect to restrictions on transfer of their equity securities, preemptive rights on future issuances of capital stock and other securities by Holdings, voting rights and registration rights. In addition, Holdings, together with its wholly-owned subsidiary, US Oncology, Inc. (“US Oncology”), its subsidiaries, and its existing lenders entered into Amendment No. 4 to the Credit Agreement, dated as of August 20, 2004, as amended, among US Oncology, Holdings, JPMorgan Chase Bank, N.A., as administrative agent and collateral agent, the lenders from time to time party thereto, Wachovia Bank, National Association, as syndication agent, and Citicorp North America, Inc., as documentation agent, to, among other things, permit the consummation of the foregoing investment and the use of proceeds from the investment described in Item 3.02 below.

Copies of the Stock Purchase Agreement, the Amended and Restated Stockholders Agreement, the Amended and Restated Registration Rights Agreement and Amendment No. 4 to the Credit Agreement are attached hereto as Exhibits 10.1, 10.2, 10.3 and 10.4, respectively. The descriptions of the foregoing documents set forth herein do not purport to be complete and are qualified in their entirety by the provisions of such documents attached hereto.

ITEM 3.02 UNREGISTERED SALES OF EQUITY SECURITIES

The investment by Morgan Stanley described in Item 1.01 above was a private placement transaction exempt from registration under the Securities Act of 1933, as amended (the “1933 Act”), pursuant to Section 4(2) of the 1933 Act and Regulation D promulgated thereunder.

The net proceeds of the foregoing investment, together with certain cash-on-hand of US Oncology, will be used to pay a dividend of up to $190 million on the outstanding common stock (including the shares of outstanding participating preferred stock to the extent such shares participate with common stock in such dividends) of Holdings and pay related fees and expenses. The dividend will be paid on or about January 3, 2007. The shares acquired by Morgan Stanley were acquired after the record date for the dividend and therefore will not receive any proceeds of the dividend.

In connection with the consummation of the foregoing investment, Holdings amended and restated its certificate of incorporation to, among other things, increase its authorized capital stock and create a new series of its participating preferred stock to be issued to Morgan Stanley. The new series of participating preferred stock has terms which are substantially similar to, and ranks on par with, Holdings’ existing series of participating preferred stock. Both series of the participating preferred stock of Holdings rank senior to Holdings common stock as to dividends and rights to payment upon liquidation or a change of control transaction and will participate with the common stock in such payments and other corporate events. The participating preferred stock is also entitled to receive cumulative dividends on a non-cash accrual basis at a rate equal to 7% per annum, compounded quarterly, on the stated value thereof. The participating preferred stock has no fixed redemption date, but is subject to mandatory redemption upon a change of control transaction. In the event of a qualified initial public offering of the common stock of Holdings or US Oncology, each share of the participating preferred stock will automatically convert into Holdings common stock through the issuance of an equivalent value of Holdings common stock determined by reference to the public offering price and a fixed conversion ratio of shares of common stock issuable in respect of the participation feature of the participating preferred stock. At that time, Holdings has the option to redeem all of the shares of common stock issued upon conversion of the participating preferred stock, other than shares issued in respect of the participation feature. The participating preferred stock votes together with the shares of Holdings common stock, with each share of participating preferred stock currently receiving 1 vote per share. In addition, each series of the participating preferred stock has certain separate voting rights with respect to certain corporate events and other matters.

A copy of the Second Amended and Restated Certificate of Incorporation of Holdings setting forth the rights, preferences and privileges of its participating preferred stock and common stock is attached hereto as Exhibit 3.1. The description of such document set forth herein does not purport to be complete and is qualified in its entirety by the provisions of such document attached hereto.

ITEM 5.02 DEPARTURE OF DIRECTORS OR PRINCIPAL OFFICERS; ELECTION OF DIRECTORS; APPOINTMENT OF PRINCIPAL OFFICERS

In connection with the consummation of the foregoing investment, Holdings increased the size of its board of directors by 1, and added William T. Reiland as a new board member. Mr. Reiland has been a managing director at Morgan Stanley & Co. Incorporated since December 2004. He currently works in the Principal Investments group within the Fixed Income Division. Mr. Reiland joined Morgan Stanley & Co. Incorporated in 1993, initially as an investment banker covering hospital, physician group and HMO companies and has held various positions since that time.

Other than as described in this Current Report, there are no other transactions in which Mr. Reiland has an interest requiring disclosure pursuant to Item 404(a) of Regulation S-K. Pursuant to the Amended and Restated Stockholders Agreement, Mr. Reiland has been designated by Morgan Stanley to serve on the Holdings board of directors.

ITEM 9.01 FINANCIAL STATEMENTS AND EXHIBITS

(c) Exhibits

Exhibit		Document
3.1	-	Second Amended and Restated Certificate of Incorporation of Holdings
10.1	-	Stock Purchase Agreement, dated as of December 21, 2006
10.2	-	Amended and Restated Stockholders Agreement, dated as of December 21, 2006
10.3	-	Amended and Restated Registration Rights Agreement, dated as of December 21, 2006
10.4	-	Fourth Amendment to Credit Agreement, dated December 21, 2006
99.1	-	Press Release, dated December 22, 2006

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, each of Holdings and US Oncology have duly caused this Current Report to be signed on its behalf by the undersigned hereunto duly authorized.

	US ONCOLOGY HOLDINGS, INC.
Dated: December 22, 2006	By:	/s/ Phillip H. Watts
	Name:	Phillip H. Watts
	Title:	Vice President and General Counsel
	US ONCOLOGY, INC.
Dated: December 22, 2006	By:	/s/ Phillip H. Watts
	Name:	Phillip H. Watts
	Title:	Vice President and General Counsel

EXHIBIT INDEX

Exhibit		Document
3.1	-	Second Amended and Restated Certificate of Incorporation of Holdings
10.1	-	Stock Purchase Agreement, dated as of December 21, 2006
10.2	-	Amended and Restated Stockholders Agreement, dated as of December 21, 2006
10.3	-	Amended and Restated Registration Rights Agreement, dated as of December 21, 2006
10.4	-	Fourth Amendment to Credit Agreement, dated December 21, 2006
99.1	-	Press Release, dated December 22, 2006

EX-3.1

Exhibit 3.1

SECOND AMENDED AND RESTATED

CERTIFICATE OF INCORPORATION

OF

US ONCOLOGY HOLDINGS, INC.,

a Delaware corporation

US ONCOLOGY HOLDINGS, INC., a corporation organized and existing under the General Corporation Law of the State of Delaware (the “Corporation”)

DOES HEREBY CERTIFY:

1. That the name of the Corporation is US Oncology Holdings, Inc. The name under which the Corporation was originally incorporated is Oiler Holding Company. The original Certificate of Incorporation of the Corporation was filed with the Secretary of State of Delaware on March 17, 2004. An Amended and Restated Certificate of Incorporation was filed with the Secretary of State of Delaware on August 19, 2004.

2. That pursuant to Sections 228, 242 and 245 of the General Corporation Law of the State of Delaware, this Second Amended and Restated Certificate of Incorporation amends and restates the provisions of the Amended and Restated Certificate of Incorporation of the Corporation in its entirety.

3. That the Board of Directors of the Corporation, at a meeting on December 20, 2006 adopted resolutions setting forth a proposed amendment and restatement of the Amended and Restated Certificate of Incorporation of the Corporation in the form hereof, declaring said amendment and restatement to be advisable and in the best interests of the Corporation and its stockholders and submitting the proposed amendment and restatement to the stockholders of the Corporation for consideration thereof.

4. That this Second Amended and Restated Certificate of Incorporation was approved by written consent of the stockholders of the Corporation dated December 20, 2006.

5. That the text of the Amended and Restated Certificate of Incorporation of the Corporation is hereby amended and restated to read in its entirety as follows:

FIRST: The name of the Corporation is US Oncology Holdings, Inc.

SECOND: The address of the registered office of the Corporation in the State of Delaware is 2711 Centerville Road, Suite 400, in the City of Wilmington, County of New Castle 19808. The name of the Corporation’s registered agent at such address is Corporation Service Company.

THIRD: The purpose of the Corporation is to engage in any lawful act or activity for which a corporation may be organized under the General Corporation Law of the State of Delaware (the “DGCL”).

FOURTH: The total number of shares of all classes of stock which the Corporation shall have authority to issue is 317,000,000, consisting of (i) 300,000,000 shares of Common Stock, par value $0.001 per share (the “Common Stock”), and (ii) 17,000,000 shares of Participating Preferred Stock, par value $0.001 per share (the “Participating Preferred Stock”).

The following is a statement of the powers, preferences and rights, and the qualifications, limitations and restrictions thereof, in respect of each class of stock of the Corporation:

I. Participating Preferred Stock

1. Series; Rank.

(a) The Participating Preferred Stock shall be divided into two series consisting of shares of Series A Participating Preferred Stock (the “Series A Preferred Stock”) and shares of Series A-1 Participating Preferred Stock (the “Series A-1 Preferred Stock”). The Series A Preferred Stock shall include all shares of Participating Preferred Stock issued and outstanding prior to the date hereof as well as any additional shares of Participating Preferred Stock that are issued on or after the date hereof to the extent such shares are designated to be Series A Preferred Stock by the Board of Directors of the Corporation at the time such shares are issued. The Series A-1 Preferred Stock shall include up to 2,000,000 shares of Participating Preferred Stock that are issued on or after the date hereof to the extent such shares are designated to be Series A-1 Preferred Stock by the Board of Directors of the Corporation at the time such shares are issued. Unless otherwise indicated herein, both the Series A Preferred Stock and the Series A-1 Preferred Stock shall be considered the same class of stock of the Corporation and shall, with respect to dividend rights, redemption and rights to distributions upon any liquidation, dissolution or winding up of the Corporation rank on par to each other and be treated identically (other than differences that may result from differences in the Accreted Value of such shares).

(b) The Participating Preferred Stock shall, with respect to dividend rights (other than rights to Participating Dividends (as defined below)) and, unless otherwise set forth herein, rights to distributions upon any liquidation, dissolution or winding up of the Corporation, rank senior to the Common Stock and to each other class or series of capital stock of the Corporation now or hereafter established (collectively, “Junior Stock”).

2. Dividends.

(a) Cumulative dividends shall accrue on each outstanding share of Participating Preferred Stock on each day from and after the date of issue of such share at a rate per annum equal to 7% of the Unpaid Base Amount (as defined below) of such share (such

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dividends, “Regular Dividends”). Regular Dividends on each share of Participating Preferred Stock shall compound (i.e., be added to the Unpaid Base Amount of such share) quarterly on July 31, October 31, January 31, April 30 of each year (each a “Dividend Compounding Date”). Regular Dividends shall accrue on each share of Participating Preferred Stock whether or not declared and whether or not there are any funds of the Corporation legally available for the payment of dividends, and shall be computed on the basis of the actual number of days elapsed in a year of 365 or 366 days, as applicable. Subject to paragraph 8 below, Regular Dividends shall be payable in cash if permitted by the Credit Agreement (as defined below) only (i) upon a liquidation, dissolution or winding-up of the Corporation, (ii) upon a redemption pursuant to paragraph 3 below or (iii) if holders of not less than a majority of the outstanding shares of Participating Preferred Stock so elect pursuant to paragraph 5(d) below in connection with a conversion of the Participating Preferred Stock to Common Stock, upon such conversion pursuant to paragraph 5 below. If holders of a majority of the outstanding shares of Participating Preferred Stock consent thereto in writing, Regular Dividends may be paid when due in a form other than cash as determined by the Board of Directors.

(b) As used herein, (i) “Accreted Value” means, with respect to any share of Participating Preferred Stock as of any date of determination, the sum of (A) the Unpaid Base Amount (as defined below) of such share as of such date of determination and (B) the amount of accrued but unpaid Regular Dividends thereon since the most recent Dividend Compounding Date (or, if prior to the first Dividend Compounding Date, the date of issue of such share) and (ii) “Unpaid Base Amount” means, (A) with respect to any share of Series A Preferred Stock, (1) $32 plus (2) the aggregate amount of accrued but unpaid Regular Dividends added to the Unpaid Base Amount of such share on each Dividend Compounding Date since the date of issue of such share in accordance with paragraph 2(a) above minus (3) the sum of all amounts previously declared in respect of such share as Special Dividends (as defined in paragraph 2(e) below), and (B) with respect to any share of Series A-1 Preferred Stock, (1) $21.4475 plus (2) the aggregate amount of accrued but unpaid Regular Dividends added to the Unpaid Base Amount of such share on each Dividend Compounding Date since the date of issue of such share in accordance with paragraph 2(a) above minus (3) the sum of all amounts previously declared in respect of such share as Special Dividends (as defined in paragraph 2(e) below). For avoidance of doubt, as of January 31, 2007, after giving effect to the compounding of Regular Dividends on such date (and assuming no payment of any Regular Dividends or Special Dividends after December 21, 2006 and prior to such date), each share of Series A Preferred Stock issued on August 20, 2004 and each share of Series A-1 Preferred Stock issued on December 21, 2006 shall have an Accreted Value equal to approximately $21.6145 (subject only to de minimis differences due solely to rounding).

(c) The date on which the Corporation initially issues any particular share of Participating Preferred Stock shall be deemed to be its “date of issue” for purposes hereof regardless of the number of times transfer of such share is made on the stock records maintained by or for the Corporation and regardless of the number of certificates that may be issued to evidence such share.

(d) Unless the Unpaid Base Amount of each outstanding share of Participating Preferred Stock has been reduced to $0 and all accrued or declared dividends thereon have been paid in full, the Corporation shall not declare or pay any dividend or make any distribution in

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respect of (other than dividends or distributions on the Common Stock payable solely in Common Stock), or redeem, repurchase or otherwise acquire for any consideration (or cause any subsidiary of the Corporation to redeem, repurchase or otherwise acquire for any consideration), any Junior Stock without the prior written consent of holders of not less than a majority of the then outstanding shares of Participating Preferred Stock. In case the Corporation shall make any dividend or distribution to holders of Common Stock that is permitted under this paragraph 2(d), whether payable in cash, securities or other property (other than dividends or distributions on the Common Stock payable solely in Common Stock), the holder of each share of Participating Preferred Stock on the record date for such dividend or distribution shall be entitled to receive an equivalent dividend or distribution (“Participating Dividends”) based on the number of shares of Common Stock then outstanding (assuming for such purposes that each share of Participating Preferred Stock was converted into a number of shares of Common Stock equal to the Conversion Constant (as defined in paragraph 5(b) below) immediately prior to the record date for such dividend or other distribution even though such conversion does not actually occur).

(e) The holders of shares of Participating Preferred Stock shall be entitled to receive Special Dividends as from time to time may be declared by the Board of Directors of the Corporation out of funds legally available therefor. As used herein, “Special Dividends” means all distributions made by the Corporation to holders of Participating Preferred Stock in respect of the Participating Preferred Stock, whether by dividend or otherwise (including without limitation any distributions made by the Corporation to holders of Participating Preferred Stock in partial liquidation of the Corporation); provided, that the following shall be excluded from the definition of Special Dividends: (i) Regular Dividends, (ii) Participating Dividends, (iii) any redemption or repurchase by the Corporation of any shares of Participating Preferred Stock for any reason, (iv) any recapitalization, reclassification or exchange of any shares of Participating Preferred Stock, except to the extent that property other than capital stock of the Corporation (including cash or debt securities) is received in respect of any shares of Participating Preferred Stock in any such transaction, (v) any subdivision or increase in the number of (by stock split, stock dividend or otherwise), or any combination in any manner of, any outstanding shares of stock of the Corporation, (vi) a merger, share exchange or consolidation involving the Corporation, except to the extent that property other than capital stock of the Corporation (including cash or debt securities) is received in respect of any shares of Participating Preferred Stock in any such transaction, or (vii) any liquidation, dissolution or winding up of the Corporation.

3. Redemption Upon a Change of Control.

(a) Subject to paragraph 8 below, and except as and to the extent prohibited by applicable law, the Corporation shall redeem all shares of Participating Preferred Stock then outstanding for the consideration and in the manner and with the effect provided in this paragraph 3 upon the occurrence of a Change of Control (as defined below). As used herein, the following terms shall have the following meanings:

“Affiliate” of any specified Person means any other Person directly or indirectly controlling or controlled by or under direct or indirect common control with such specified Person. For the purposes of this definition, “control” when used with respect to any Person means the power to direct the management and policies of such Person, directly or indirectly, whether through the ownership of voting securities, by contract or otherwise; and the terms “controlling” and “controlled” have meanings correlative to the foregoing.

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“Capital Stock” means, with respect to any Person, any shares or other equivalents (however designated) of any class of corporate stock or partnership interests or any other participations, rights, warrants, options or other interests in the nature of an equity interest in such Person, including Preferred Stock, but excluding any debt security convertible or exchangeable into such equity interest.

“Change of Control” means the occurrence of any of the following events:

(a) prior to the earlier to occur of the first public equity offering of common stock of the Corporation or US Oncology, Inc. (“US Oncology”), the WCAS Holders cease to be the “beneficial owners” (as defined in Rule 13d-3 under the Securities and Exchange Act of 1934, as amended (the “Exchange Act”), except that a Person will be deemed to have “beneficial ownership” of all shares that any such Person has the right to acquire, whether such right is exercisable immediately or only after the passage of time), directly or indirectly, of a majority of the total voting power of the Voting Stock of the Corporation or US Oncology, whether as a result of the issuance of securities of the Corporation or US Oncology, any merger, consolidation, liquidation or dissolution of the Corporation or US Oncology, any direct or indirect transfer of securities by the Corporation, the WCAS Holders or otherwise (for purposes of this clause (a), the WCAS Holders will be deemed to beneficially own any Voting Stock of a Person (the “specified person”) held by any other Person (the “parent entity”) so long as the WCAS Holders beneficially own, directly or indirectly, in the aggregate a majority of the total voting power of the Voting Stock of such parent entity);

(b) on or after the earlier to occur of the first public equity offering of common stock of the Corporation or US Oncology, if any “person” or “group” (as such terms are used in Sections 13(d) and 14(d) of the Exchange Act or any successor provisions to either of the foregoing), including any group acting for the purpose of acquiring, holding, voting or disposing of securities within the meaning of Rule 13d-5(b)(1) under the Exchange Act, other than any one or more of the WCAS Holders, becomes the “beneficial owner” (as defined in clause (a) above), directly or indirectly, of 35% or more of the total voting power of the Voting Stock of the Corporation or US Oncology; provided, however, that the WCAS Holders are the “beneficial owners” (as defined in clause (a) above), directly or indirectly, in the aggregate of a lesser percentage of the total voting power of the Voting Stock of the Corporation or US Oncology than such other person or group and do not have the right or ability by voting power, contract or otherwise to elect or designate for election a majority of the Board of Directors of the Corporation or US Oncology (for purposes of this clause (b), such person or group shall be deemed to beneficially own any Voting Stock of a specified person held by a parent entity, so long as such person or group beneficially owns, directly or indirectly, in the aggregate a majority of the total voting power of the Voting Stock of such parent entity and the WCAS Holders do not have the right

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or ability by voting power, contract or otherwise to elect or designate for election a majority of the board of directors of such parent entity);

(c) the sale, lease, transfer or other conveyance, in one or a series of related transactions, of all or substantially all of the assets of the Corporation and its subsidiaries, taken as a whole, or US Oncology and its Subsidiaries, taken as a whole, to any Person other than one or more WCAS Holders; or

(d) during any period of two consecutive calendar years, individuals who at the beginning of such period constituted the Board of Directors of US Oncology or the Board of Directors of the Corporation (together with any new directors whose election or appointment by the Board of Directors of US Oncology or the Board of Directors of the Corporation or whose nomination for election by the shareholders of US Oncology or the Corporation was approved by (i) a vote of not less than a majority of the directors then still in office who were either directors at the beginning of such period or whose election or nomination for election was previously so approved or (ii) WCAS Holders) cease for any reason to constitute a majority of the Board of Directors of US Oncology or the Board of Directors of the Corporation then in office, provided that for purposes of this clause (d), the terms “Board of Directors of US Oncology” and “Board of Directors of the Corporation” shall not include any committee thereof.

“Person” means any individual, corporation, company (including any limited liability company), association, partnership, joint venture, trust, unincorporated organization, government or any agency or political subdivision thereof or any other entity.

“Preferred Stock” means any Capital Stock of a Person, however designated, which entitles the holder thereof to a preference with respect to the payment of dividends, or as to the distribution of assets upon any voluntary or involuntary liquidation or dissolution of such Person, over shares of any other class of Capital Stock issued by such Person.

“Related Parties” means, with respect to any specified Person at any specified time,

(1) if a natural person, (A) any spouse, parent or lineal descendant (including by adoption) of such Person or (B) the estate of such Person during any period in which such estate holds Capital Stock of the Corporation or of US Oncology for the benefit of any Person referred to in clause (1)(A), and

(2) if a trust, corporation, partnership, limited liability company or other entity, any other Person that controls such Person at such time. For the purposes of this definition, “control” when used with respect to any Person means the power to direct the management and policies of such Person, directly or indirectly, whether through the ownership of voting securities, by contract or otherwise.

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“Subsidiary” means, in respect of any Person, any corporation, company (including any limited liability company), association, partnership, joint venture or other business entity of which a majority of the total voting power of the Voting Stock is at the time owned or controlled, directly or indirectly, by:

(a) such Person,

(b) such Person and one or more Subsidiaries of such Person, or

(c) one or more Subsidiaries of such Person.

“Voting Stock” of any Person means all classes of Capital Stock or other interests (including partnership interests) of such Person then outstanding and normally entitled (without regard to the occurrence of any contingency) to vote in the election of directors, managers or trustees thereof.

“WCAS Holders” means (i) Welsh, Carson, Anderson & Stowe IX, L.P. and its Affiliates (including, without limitation, any investment partnership under common control with Welsh, Carson, Anderson & Stowe IX, L.P.), (ii) any officer, director, employee, partner, member or stockholder of the manager or general partner of the foregoing Persons and (iii) any Related Parties with respect to any of the foregoing Persons.

(b) For each share of Participating Preferred Stock to be redeemed pursuant to this paragraph 3 on the date of the consummation of the Change of Control (the “Redemption Date”) the Company shall:

(i) pay the Base Redemption Amount (as defined below) and

(ii) issue a number of fully paid and non-assessable whole shares of Common Stock (the “Redemption Shares”) equal to the Conversion Constant (as defined in Section 5(b) below) then in effect.

As used herein, the term “Base Redemption Amount” means, with respect to any share of Participating Preferred Stock subject to redemption, the sum of:

(A) the Accreted Value of such share as of the date of redemption,

plus

(B) the amount of declared but unpaid dividends thereon (including any declared but unpaid Special Dividends or Participating Dividends) other than Regular Dividends through and including the date of redemption.

(c) The Base Redemption Amount shall be paid on the Redemption Date in cash unless (i) the holders of the Common Stock are to receive non-cash consideration in connection with the Change of Control transaction, (ii) the Board of Directors determines that

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the Corporation does not have adequate cash to pay the Base Redemption Amount (it being understood that the Corporation shall remain obligated to pay the Base Redemption Amount in cash to the extent of available cash) and (iii) (A) in the case of the Series A Preferred Stock, the holders of a majority of the outstanding Series A Preferred Stock consent in writing to the payment of all or a portion of the remaining Base Redemption Amount of the Series A Preferred Stock in non-cash consideration or (B) in the case of the Series A-1 Preferred Stock, the holders of a majority of the outstanding Series A-1 Preferred Stock consent in writing to the payment of all or a portion of the remaining Base Redemption Amount of the Series A-1 Preferred Stock in non-cash consideration. In such event, the Corporation may pay the Base Redemption Amount in whole or in part in non-cash consideration so long as (x) (A) the holders of the Series A Preferred Stock receive the same form of non-cash consideration as the holders of the Common Stock on the same terms and conditions as such other stockholders or (B) the holders of the Series A-1 Preferred Stock receive the same form of non-cash consideration as the holders of the Common Stock on the same terms and conditions as such other stockholders, as the case may be, and (y) no holder of Common Stock receives a higher percentage of cash consideration for its shares of Common Stock than (A) the holders of the Series A Preferred Stock receive for their shares of Series A Preferred Stock or (B) the holders of Series A-1 Preferred Stock receive for their shares of Series A-1 Preferred Stock.

(d) Any Redemption Shares issued in connection with a redemption of the Participating Preferred Stock pursuant to this Section 3 shall be deemed to be issued and outstanding at the time of the related Change of Control transaction and shall be entitled to receive (on a pro rata basis and on the same terms and conditions) the same consideration per share as is payable in connection with such Change of Control transaction in respect of the other shares of Common Stock then issued and outstanding.

(e) No less than ten days before the Redemption Date, written notice shall be given by mail, postage prepaid to the holders of record of the Participating Preferred Stock specifying the place and date of such redemption, which date shall not be a day on which banks in the City of New York, New York or the City of Houston, Texas are required or authorized to close. If such notice of redemption shall have been duly given and if on or before the Redemption Date the funds necessary for redemption shall have been set aside so as to be and continue to be available therefor, then, notwithstanding that any certificate for shares of Participating Preferred Stock to be redeemed shall not have been surrendered for cancellation, after 5:00 p.m. (New York time) on the Redemption Date, the shares so called for redemption shall no longer be deemed outstanding, any dividends thereon shall cease to accrue, and all rights with respect to such shares shall forthwith after 5:00 p.m. (New York time) on the Redemption Date cease, except for the right of the holders thereof to receive, upon presentation of the certificate representing shares so called for redemption, the Base Redemption Amount therefor, without interest thereon, and the Redemption Shares.

(f) Any shares of Participating Preferred Stock redeemed pursuant to this paragraph 3 or otherwise repurchased or acquired by the Corporation in any manner whatsoever shall be retired and canceled promptly after the acquisition thereof.

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(g) In the event that, for any reason, only a portion of the outstanding shares of Participating Preferred Stock are redeemed on the Redemption Date, the shares of Participating Preferred Stock to be redeemed on such date shall be selected on a pro rata basis and there shall be redeemed from each registered holder of Participating Preferred Stock that proportion of all of the shares to be redeemed on such date which the number of shares held of record by such holder bears to the total number of shares of such Participating Preferred Stock at the time outstanding. Any shares of Participating Preferred Stock required to be but not redeemed for any reason on any Redemption Date shall be redeemed as soon thereafter as possible and in the manner in which shares are otherwise required to be redeemed on such Redemption Date, and, in such event, such shares shall continue to have all rights of Participating Preferred Stock until redeemed.

4. Liquidation; Dissolution or Winding-Up of the Corporation.

(a) Subject to paragraph 8 below, upon any liquidation, dissolution or winding up of the Corporation, whether voluntary or involuntary, the holders of the shares of Participating Preferred Stock shall be entitled to:

(A) be paid, before distribution or payment is made upon any outstanding Junior Stock, an amount equal to the sum of

(i) the Accreted Value of each share of Participating Preferred Stock held of record by such holder as of the time of payment

plus

(ii) the amount of declared but unpaid dividends thereon (including any declared but unpaid Special Dividends or Participating Dividends) other than Regular Dividends through and including the time of payment, and

(B) thereafter, participate ratably with the holders of the Common Stock in any distribution of the remaining assets of the Corporation, or proceeds thereof, available for distribution to the stockholders of the Corporation based on the number of shares of Common Stock then outstanding (assuming for such purposes that each share of Participating Preferred Stock was converted into a number of shares of Common Stock equal to the Conversion Constant (as defined in paragraph 5(b) below) immediately prior to such liquidation, dissolution or winding-up of the Corporation even though such conversion does not actually occur).

(b) Written notice of any such liquidation, dissolution or winding up, stating a payment date, the amount of the liquidation payments and the place where said liquidation payments shall be payable, shall be given by mail, postage prepaid, not less than 20 days prior to the payment date stated therein, to the holders of record of Participating Preferred Stock, such notice to be addressed to each such holder at its post office address as shown by the records of the Corporation.

9

(c) If, upon any such liquidation, dissolution or winding up of the Corporation, the assets of the Corporation, or proceeds thereof, distributable among the holders of the Participating Preferred Stock shall be insufficient to pay in full the preferential amount due on such shares, then such assets, or the proceeds thereof, shall be distributed to the holders of the Participating Preferred Stock ratably in accordance with the respective amounts that would be payable on such shares of Participating Preferred Stock if all amounts thereon were paid in full.

(d) Neither the sale, lease, transfer, conveyance or other disposition, in one or a series of related transactions, of all or substantially all the assets of the Corporation and its subsidiaries taken as a whole nor the consummation of any merger, consolidation, recapitalization or reorganization of the Corporation shall be deemed to be a liquidation, dissolution or winding-up of the Corporation for purposes of this paragraph 4.

(e) In connection with any liquidation, dissolution or winding-up of the Corporation, the amounts payable to the holders of Participating Preferred Stock may be paid in a form other than cash (the value thereof to be determined in good faith by the Board of Directors of the Corporation) only if holders of a majority of the then outstanding shares of Participating Preferred Stock consent thereto (and to such valuation) in writing.

5. Automatic Conversion of the Participating Preferred Stock Upon Pricing of a Qualified IPO; Redemption of Conversion Shares.

(a) Subject to and upon the terms and conditions of this paragraph 5, and, if necessary, subject to compliance with the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, at the Qualified IPO Pricing Time (as defined below), each outstanding share of Participating Preferred Stock shall be automatically converted, without further action on the part of the Corporation or any holder of Participating Preferred Stock, into that number of fully paid and non-assessable whole shares of Common Stock (such number, the “Conversion Factor”) equal to the sum of:

(i) the quotient obtained by dividing

(x) the sum of:

(1) Accreted Value of such share determined at the time of such conversion,

plus

(2) the amount of declared but unpaid dividends thereon (including any declared but unpaid Special Dividends or Participating Dividends) other than Regular Dividends through and including the time of conversion (such sum, the “Conversion Value”),

by

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(y) the offering price per share of Common Stock to be received by the Corporation in the Qualified IPO (as hereinafter defined) taking into account any subdivision, increase or combination of the Common Stock in connection with such offering (the “IPO Sale Price”);

plus

(ii) the Conversion Constant (as defined in paragraph 5(b) below) determined at the time of such conversion;

provided, that, if the holders of not less than a majority of the outstanding shares of Participating Preferred Stock have elected pursuant to paragraph 5(d) below to receive cash in payment of (x) all accrued but unpaid Regular Dividends on each share of Participating Preferred Stock since the most recent Dividend Compounding Date (or, if prior to the first Dividend Compounding Date, the date of issue of such share of Participating Preferred Stock) and (y) all other declared but unpaid dividends (including any declared but unpaid Special Dividends or Participating Dividends) on each share of Participating Preferred Stock in connection with the conversion thereof, the Conversion Factor with respect to such conversion of each share of Participating Preferred Stock shall mean the sum of:

(i) the quotient obtained by dividing

(x) the Conversion Value of such share, reduced by the amount of dividends with respect to such share that the holders of Participating Preferred Stock have elected to receive in cash

by

(y) the IPO Sale Price,

plus

(ii) the Conversion Constant (as defined in paragraph 5(b) below) determined at the time of such conversion,

(b) As used herein, the following terms shall have the following meanings:

“Conversion Constant” means, with respect to each share of Participating Preferred Stock, one (1), as from time to time adjusted pursuant to paragraphs 5(h) and 5(i) below.

“Qualified IPO” means the sale of Common Stock by the Corporation or US Oncology to the public in a firm commitment underwritten public offering pursuant to an effective registration statement (other than a registration statement on Form S-4 or Form S-8 or any similar successor form) filed under the Securities Act of 1933, as

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amended (the “Securities Act”), in which the aggregate proceeds to the Corporation or US Oncology (together with the aggregate proceeds in all such prior public offerings) are at least $100,000,000.

(c) The conversion of Participating Preferred Stock to Common Stock pursuant to this paragraph 5 shall be effected concurrently with, and the Conversion Factor applicable to any such conversion shall be determined concurrently with, the determination by the Corporation of the IPO Sale Price (the “Qualified IPO Pricing Time”) and prior to the completion of any registration of any class of equity securities of the Corporation pursuant to Section 12 of the Exchange Act or any transfer of beneficial ownership of shares in connection with any such offering. At the effective time of such conversion, the rights of the holders of the Participating Preferred Stock shall cease and the Persons in whose names the certificates for such shares are registered shall be deemed to have become the holders of record of the shares of Common Stock issuable upon conversion thereof (the “Conversion Shares”). Promptly after the effectiveness of any conversion of Participating Preferred Stock to Common Stock pursuant to this paragraph 5, the Corporation shall issue and deliver, or cause to be issued and delivered, to the appropriate holders, registered in such names as such holders may direct, subject to compliance with applicable laws to the extent such designation shall involve a transfer, and subject to the surrender by such holders of the certificates for the shares of the Participating Preferred Stock so converted, certificates for the number of Conversion Shares issuable upon the conversion of such shares of Participating Preferred Stock. The rights of stockholders to receive certificates representing Conversion Shares shall be subject to the surrender of such certificates to the Corporation.

(d) Notwithstanding anything to the contrary contained herein, if the holders of not less than a majority of the outstanding shares of Participating Preferred Stock so elect in a writing delivered to the Corporation, upon conversion of each share of Participating Preferred Stock pursuant to this paragraph 5, (x) all accrued but unpaid Regular Dividends on such share of Participating Preferred Stock since the most recent Dividend Compounding Date (or, if prior to the first Dividend Compounding Date, the date of issue of such share of Participating Preferred Stock) and (y) all other declared but unpaid dividends (including any declared but unpaid Special Dividends or Participating Dividends) on each share of Participating Preferred Stock shall be paid to the holders of the Participating Preferred Stock on the date such conversion is effective (determined in accordance with paragraph (c) above).

(e) No fractional shares shall be issued upon conversion of the Participating Preferred Stock into Common Stock. If any fractional interest in a share of Common Stock would, except for the provisions of the first sentence of this paragraph 5(e), be deliverable upon any such conversion, the Corporation, in lieu of delivering the fractional share thereof, shall pay to the holder surrendering the Participating Preferred Stock for conversion an amount in cash equal to the fair value of such fractional share (determined by reference to the IPO Sale Price).

(f) Subject to paragraph 6(f) and paragraph 8 below, and except as and to the extent prohibited by applicable law, on the closing date of the Qualified IPO (the “Qualified IPO Closing Date”), the Corporation shall have the option to redeem from the holders of the Conversion Shares up to that number of Conversion Shares equal to the Share Number (as

12

defined below) for the consideration and in the manner and with the effect provided in this paragraph 5(f) and paragraph 5(g). The redemption price payable for all Conversion Shares redeemed under this paragraph 5(f) shall be payable in cash and shall be equal to the IPO Sale Price. As used herein, “Share Number” means (x) the number of Conversion Shares that would have been issued pursuant to paragraph 5(a) in connection with the Qualified IPO had the Conversion Constant been zero (0) at the time the Conversion Factor was determined less (y) the number of Conversion Shares, if any, sold by holders thereof (other than the Corporation) in the Qualified IPO.

(g) The rights of holders of Conversion Shares called for redemption to receive the redemption price payable under paragraph 5(f) shall be subject to the surrender of the certificates representing such shares. If on or before the Qualified IPO Closing Date the funds necessary for any redemption under paragraph 5(f) shall have been set aside so as to be and continue to be available therefor, then, notwithstanding that any certificate representing Conversion Shares shall not have been surrendered for cancellation, after 5:00 p.m. (New York time) on the Qualified IPO Closing Date, the Conversion Shares subject to redemption on the Qualified IPO Date shall no longer be deemed outstanding and all rights with respect to such shares shall forthwith after 5:00 p.m. (New York time) on such date cease, except for the right of the holders thereof to receive, upon presentation of the certificates representing the Conversion Shares called for redemption, the redemption price for such shares, without interest thereon. Conversion Shares to be redeemed on the Qualified IPO Closing Date shall be selected for redemption on a pro rata basis and there shall be redeemed from each registered holder thereof that proportion of all of the Conversion Shares to be redeemed on such date which the number of Conversion Shares held of record by such holder bears to the total number of Conversion Shares.

(h) The Corporation shall not in any manner subdivide or increase the number of (by stock split, stock dividend or other similar manner), or combine in any manner, the outstanding shares of Participating Preferred Stock. The Corporation shall not in any manner subdivide or increase the number of (by stock split, stock dividend or other similar manner), or combine in any manner, any class of outstanding Common Stock unless a proportional adjustment is made to the Conversion Constant.

(i) If any capital reorganization or reclassification of the capital stock of the Corporation shall be effected in such a way (including, without limitation, by way of consolidation or merger) that holders of Common Stock shall be entitled to receive stock, securities or assets with respect to or in exchange for Common Stock, then, as a condition of such reorganization or reclassification, lawful and adequate provision shall be made whereby each holder of a share or shares of Participating Preferred Stock shall thereafter have the right to receive in connection with a Qualified IPO, upon the basis and upon the terms and conditions specified herein and in lieu of the shares of Common Stock immediately theretofore receivable upon the conversion of such share or shares of the Participating Preferred Stock, such shares of stock, securities or assets as may be issued or payable with respect to or in exchange for a number of outstanding shares of such Common Stock equal to the number of shares of such stock immediately theretofore so receivable had such reorganization or reclassification not taken place, and in any such case appropriate provision shall be made with respect to the rights and interests of such holder to the end that the provisions hereof shall thereafter be applicable, as

13

nearly as may be, in relation to any shares of stock, securities or assets thereafter deliverable upon the exercise of such conversion rights. In the event of a merger or consolidation of the Corporation as a result of which a greater or lesser number of shares of common stock of the surviving corporation are issuable to holders of Common Stock immediately prior to such merger or consolidation, the Conversion Constant in effect immediately prior to such merger or consolidation shall be adjusted in the same manner as though there were a subdivision or combination of the outstanding shares of Common Stock.

(j) All shares of Common Stock which shall be issued upon conversion of the Participating Preferred Stock shall be duly and validly issued and fully paid and non-assessable shares of Common Stock. The issuance of certificates for shares of Common Stock upon conversion of the Participating Preferred Stock shall be made without charge to the holders thereof for any issuance tax in respect thereof; provided, that the Corporation shall not be required to pay any tax which may be payable in respect of any transfer involved in the issuance and delivery of any certificate in a name other than that of the holder of Participating Preferred Stock which is being converted.

(k) Shares of Participating Preferred Stock which are converted into shares of Common Stock as provided herein shall not be reissued.

6. Voting Rights and Restrictions.

(a) Each holder of Participating Preferred Stock shall be entitled to vote on or give or withhold consent with respect to all matters submitted to the stockholders of the Corporation for a vote or action by written consent and shall be entitled to that number of votes for each share of Participating Preferred Stock held by such holder on the record date for the determination of shareholders entitled to vote on such matter (or, if no such record date is established, on the date such vote is taken or any written consent of shareholders is solicited), as is equal to the Conversion Constant on such date; provided, that nothing contained herein shall in any way affect or restrict the rights of any holder to vote shares of any other series of capital stock of the Corporation held by such holder; provided, further, that the holders of Participating Preferred Stock will not be entitled to vote or give or withhold consent in writing pursuant to this subparagraph 6(a) in connection with the election or removal of directors to the extent the holders of the Participating Preferred Stock are then represented by Preferred Directors (as defined below) elected in accordance with subparagraph 6(b) below. Except as otherwise expressly provided herein or as required by law, the holders of shares of Participating Preferred Stock and Common Stock shall vote together as a single class on all matters.

(b) At any time when shares of Participating Preferred Stock are outstanding, the holders of the Participating Preferred Stock, voting or consenting, as the case may be, separately as a single class to the exclusion of all other shares of the Corporation’s capital stock and with each share of Participating Preferred Stock entitled to one vote, shall by plurality vote be entitled to elect two directors to the Corporation’s Board of Directors (the “Preferred Directors”).

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(c) So long as holders of the Participating Preferred Stock are entitled to elect Preferred Directors under subparagraph 6(b):

(i) the holders of the Participating Preferred Stock shall be entitled to elect such directors at any annual meeting of the stockholders (or special meeting held in place thereof);

(ii) if the holders of the Participating Preferred Stock for any reason fail to elect a person to fill any directorship to which they are otherwise entitled under subparagraph 6(b), such directorship shall remain vacant until such time as the holders of the Participating Preferred Stock elect a Preferred Director to fill such directorship and such directorship shall not be filled by resolution or vote of the Corporation’s Board of Directors or the Corporation’s other stockholders; and

(iii) any vacancy occurring because of the death, disability, resignation or removal of a Preferred Director elected by the holders of the Participating Preferred Stock shall be filled by the vote or consent of the holders of the Participating Preferred Stock.

(d)(i) At any time when shares of Series A Preferred Stock are outstanding, in addition to any other vote required by law, without the prior written consent of the holders of not less than 66 and 2/3% of the outstanding shares of Series A Preferred Stock (voting as a separate class) by vote or written consent as provided by law, (1) the Corporation will not, and will not allow any subsidiary of the Corporation to, alter or change the rights, preferences, privileges, restrictions or terms of the Series A Preferred Stock (by amendment of this Second Amended and Restated Certificate of Incorporation, merger, consolidation or otherwise) or the holders of Series A Preferred Stock with respect to such shares and (2) the Corporation will not amend this subparagraph 6(d)(i) in any respect; provided, that any amendment to this Second Amended and Restated Certificate of Incorporation which affects all shares of Participating Preferred Stock identically (other than differences that may result from differences in the Accreted Value of such shares) shall not require the consent of the holders of Series A Preferred Stock pursuant to this subparagraph 6(d)(i).

(ii) At any time when shares of Series A-1 Preferred Stock are outstanding, in addition to any other vote required by law, without the prior written consent of the holders of not less than a majority of the outstanding shares of Series A-1 Preferred Stock (voting as a separate class) by vote or written consent as provided by law, (1) the Corporation will not, and will not allow any subsidiary of the Corporation to, alter or change the rights, preferences, privileges, restrictions or terms of the Series A-1 Preferred Stock (by amendment of this Second Amended and Restated Certificate of Incorporation, merger, consolidation or otherwise) or the holders of Series A-1 Preferred Stock with respect to such shares, (2) the Corporation will not, and will not allow any subsidiary of the Corporation to, amend or waive any provision of this Second Amended and Restated Certificate or the bylaws of the Corporation in a manner that adversely affects the rights, preferences, privileges, restrictions or terms of either the Participating

15

Preferred Stock or the holders of Participating Preferred Stock with respect to such shares, and (3) the Corporation will not amend this subparagraph 6(d)(i)(ii) in any respect; provided, that any amendment which affects all shares of Participating Preferred Stock identically (other than differences that may result from differences in the Accreted Value of such shares), does not adversely effect the rights, preferences, privileges, restrictions or terms of the Series A-1 Preferred Stock or the holders of the Series A-1 Preferred Stock with respect to such shares and does not otherwise dilute the voting rights of the holders of Series A-1 Preferred Stock to vote as a separate class on certain matters set forth herein prior to or after the date of such amendment shall not require the consent of the holders of Series A-1 Preferred Stock pursuant to this subparagraph 6(d)(ii) (it being understood that any amendment that provides for the creation, authorization or issuance of any new class or series of capital stock of the Corporation that ranks on par with or junior to the Series A-1 Preferred Stock with respect to the payment of dividends, redemption payments or payment upon liquidation, dissolution or winding up of the Corporation and does not otherwise dilute the voting rights of the holders of Series A-1 Preferred Stock to vote as a separate class on certain matters set forth herein prior to or after the date of such amendment shall not require the consent of the holders of Series A-1 Preferred Stock pursuant to this subparagraph 6(d)(ii)).

(iii) If there is any proposed amendment to this Second Amended and Restated Certificate of Incorporation that affects the Series A Preferred Stock (and does not affect the Series A-1 Preferred Stock identically (other than differences that may result from differences in the Accreted Value of such shares)), the Corporation shall, at least ten (10) business days prior to such amendment taking effect, give the holders of Series A-1 Preferred Stock a copy of such amendment. The holders of Series A-1 Preferred Stock shall have the right, exercisable within ten (10) business days of receiving a copy of such amendment, by majority vote, to have an identical amendment to this Second Amended and Restated Certificate of Incorporation made as to the Series A-1 Preferred Stock. If the holders of the Series A-1 Preferred Stock exercise such right, no amendment shall take effect as to the Series A Preferred Stock unless an identical amendment shall take effect as to the Series A-1 Preferred Stock at the same time.

(e) Notwithstanding anything herein to the contrary, at any time when shares of the Participating Preferred Stock are outstanding, in addition to any other vote required by law of this Second Amended and Restated Certificate of Incorporation, without the prior written consent of the holders of not less than a majority of the outstanding shares of the Participating Preferred Stock (voting as a separate class) by vote or written consent as provided by law, the Corporation will not, and will not allow any subsidiary of the Corporation to (by amendment of this Second Amended and Restated Certificate of Incorporation, merger, consolidation or otherwise):

(i) increase or decrease (other than by redemption or conversion) the total number of authorized shares of the Participating Preferred Stock;

(ii) amend or waive any provision of this Second Amended and Restated Certificate of Incorporation or the Bylaws of the Corporation in a manner that

16

materially and adversely affects the rights, preferences or privileges of the holders of the Participating Preferred Stock;

(iii) create, obligate itself to create, authorize or issue any new class or series of capital stock of the Corporation or any security convertible into or evidencing the right to purchase shares of capital stock of the Corporation having preference over or being on parity with the Participating Preferred Stock with respect to payment of dividends (other than Participating Dividends) or payment upon liquidation, dissolution or winding-up of the Corporation;

(iv) merge or consolidate with any other entity, or enter into any transaction that would result in a Change of Control, or enter into any transaction involving a recapitalization, reclassification or exchange of any shares of Participating Preferred Stock;

(v) file any registration statement with the Securities and Exchange Commission relating to the sale of equity securities by the Corporation or its stockholders or consummate any public offering of equity securities by the Corporation; or

(vi) amend this subparagraph 6(e) in any respect.

(f) Notwithstanding anything to the contrary contained herein, in the event that the Corporation determines to pay any dividend or make any other distribution on, or redeem, repurchase or otherwise acquire, any share of capital stock or other security or interest in the Corporation other than Participating Preferred Stock, the Corporation shall not, without either (A) the written approval of the holders of a majority of the then outstanding shares of Series A Preferred Stock (or, if there is no Series A Preferred Stock then outstanding, the written approval of the holders of a majority of the Series A Preferred Stock at the time such Series A Preferred Stock was converted into Common Stock), or (B) the written approval of the holders of a majority of the then outstanding shares of Series A-1 Preferred Stock (or, if there is no Series A-1 Preferred Stock then outstanding, the written approval of the holders of a majority of the Series A-1 Preferred Stock at the time such Series A-1 Preferred Stock was converted into Common Stock), pay any dividend or make any other distribution on, or redeem, repurchase or otherwise acquire, any share of capital stock or other security or interest in the Corporation other than Participating Preferred Stock, or take any other action, so long as any share of Participating Preferred Stock is outstanding and for three years thereafter, if the effect of such dividend, distribution, redemption, repurchase, acquisition or action might be to (a) make any of the following a taxable event to the holders of the Participating Preferred Stock: (x) an increase in the Accreted Value of the Participating Preferred Stock, (y) a conversion of the Participating Preferred Stock into Common Stock or (z) an adjustment of the number of shares of Common Stock into which the Participating Preferred Stock is convertible or (b) cause any holder of Participating Preferred Stock or Conversion Shares to be subject to any liability under any applicable laws or regulations. No amendment to the provisions of this subparagraph 6(f) shall be effective without the prior written consent of the holders of a majority of the then outstanding shares of Participating Preferred Stock or, if there is no Participating Preferred Stock then

17

outstanding, the holders of a majority of the Participating Preferred Stock at the time such Participating Preferred Stock was converted into Common Stock.

(g) Notwithstanding anything to the contrary contained herein, the holders of the required majority of the outstanding Series A Preferred Stock, as specified below, shall be entitled to waive any rights of the holders of the Series A Preferred Stock without adopting an amendment to this Second Amended and Restated Certificate of Incorporation. Any such waiver shall be effective only if in writing and signed by holders of a majority of the outstanding Series A Preferred Stock, or, in the case of any such waiver of rights granted under paragraph 6(d)(i) above, 66 and 2/3% of the outstanding Series A Preferred Stock. Written notice of any such waiver shall be provided to all holders of Series A Preferred Stock (other than holders executing such waiver). For avoidance of doubt, the provisions of this subparagraph 6(g) shall not apply to any amendment to this Second Amended and Restated Certificate of Incorporation.

7. Notices.

All notices referred to herein shall be in writing, shall be delivered personally or by first class mail, postage prepaid, and shall be deemed to have been given when so delivered or mailed to the Corporation at its principal executive offices and to any stockholder at such holder’s address as it appears in the stock records of the Corporation (unless otherwise specified in a written notice to the Corporation by such holder).

8. Limitation on Redemption and Payments.

Notwithstanding anything to the contrary contained in this Second Amended and Restated Certificate of Incorporation, (i) the obligation of the Corporation to redeem or pay any amounts (including cash dividends) in respect of Participating Preferred Stock or the Conversion Shares, as the case may be, pursuant to paragraphs 3, 4 or 5 above (other than any payments solely in shares of the Corporation’s Capital Stock) shall be subordinate and subject to the terms of the Credit Agreement dated as of August 20, 2004, among the Corporation, US Oncology, the Lenders named therein and JPMorgan Chase Bank, as Administrative Agent and Collateral Agent (as amended, restated, supplemented or otherwise modified from time to time, including in connection with any refinancing or replacement thereof, the “Credit Agreement”) until such time as all Obligations (as defined in the Credit Agreement) under the Credit Agreement shall be paid in full in cash, and (ii) the obligation of the Corporation to redeem or pay any amounts (including cash dividends) in respect of Participating Preferred Stock pursuant to paragraphs 3 or 4 above in connection with a transaction resulting in a Change of Control or liquidation, dissolution or winding up of the Corporation shall not become operative until the Corporation has complied with its obligations with respect to such transaction pursuant to the terms of the Indenture, dated as of March 29, 2005, by and between the Corporation and LaSalle Bank National Association, as Trustee (as amended, restated, supplemented or otherwise modified from time to time, including in connection with any refinancing or replacement thereof, the “Indenture”). If at any time the redemption or payment of shares of Participating Preferred Stock or Common Stock would be required by paragraphs 3, 4, or 5 above, as applicable, but for the application of this paragraph 8, the Corporation shall thereafter use its best reasonable efforts to obtain as promptly as practicable thereafter any required written consents or waivers from the lenders and agents under the Credit Agreement which are necessary to permit such redemption or

18

payment, or, upon request of the holders of a majority of the outstanding shares of Participating Preferred Stock, shall use reasonable best efforts to repay all such Obligations to the extent necessary to permit such payment or redemption without such consents or waivers.

II. Common Stock

1. Dividends.

Subject to the dividend rights and preferences of the Participating Preferred Stock, the holders of shares of Common Stock shall be entitled to receive such dividends as from time to time may be declared by the Board of Directors of the Corporation out of funds legally available therefor.

2. Liquidation.

Upon any liquidation, dissolution or winding up of the Corporation, whether voluntary or involuntary, after the payment of or provision for all debts and liabilities of the Corporation and after the payment of all preferential amounts to which the holders of Participating Preferred Stock are entitled, the holders of Common Stock shall be entitled to share ratably (together with the holders of the Participating Preferred Stock to the extent set forth in paragraph 4(a)(B) of Section I of this Article FOURTH) according to the number of shares of Common Stock held by them in all remaining assets of the Corporation available for distribution to its stockholders.

3. Voting.

With respect to any matter to be voted on by the stockholders of the Corporation (other than the election of Preferred Directors), the holder of each share of Common Stock shall be entitled to one vote for each share of Common Stock held by such holder on the record date for such vote.

FIFTH: Unless and except to the extent that the Bylaws of the Corporation shall so require, the election of directors of the Corporation need not be by written ballot.

SIXTH: (a) A director of the Corporation shall not be liable to the Corporation or its stockholders for monetary damages for breach of fiduciary duty as a director, except to the extent that exculpation from liability is not permitted under the DGCL as in effect at the time such liability is determined. No amendment or repeal of this paragraph shall apply to or have any effect on the liability or alleged liability of any director of this Corporation for or with respect to any acts or omissions of such director occurring prior to such amendment or repeal.

(b) To the maximum extent permitted from time to time under the laws of the State of Delaware, this Corporation renounces any interest or expectancy of the Corporation in, or in being offered an opportunity to participate in, business opportunities that are from time to time presented to its officers, directors or stockholders, other than those officers, directors or

19

stockholders who are employees of this Corporation or its subsidiaries. No amendment or repeal of this paragraph shall apply to or have any effect on the liability or alleged liability of any officer, director or stockholder of the Corporation for or with respect to any opportunities of which such officer, director or stockholder becomes aware prior to such amendment or repeal.

SEVENTH: This Corporation shall, to the maximum extent permitted from time to time under the law of the State of Delaware, indemnify and upon request shall advance expenses to any person who is or was a party or is threatened to be made a party to any threatened, pending or completed action, suit, proceeding or claim, whether civil, criminal, administrative or investigative, by reason of the fact that such person is or was or has agreed to be a director or officer of this Corporation or while a director or officer is or was serving at the request of this Corporation as a director, officer, partner, trustee, employee or agent of any corporation, partnership, joint venture, trust or other enterprise, including service with respect to employee benefit plans, against expenses (including attorney’s fees and expenses), judgments, fines, penalties and amounts paid in settlement incurred in connection with the investigation, preparation to defend or defense of such action, suit, proceeding or claim; provided, that the foregoing shall not require this Corporation to indemnify or advance expenses to any person in connection with any action, suit, proceeding, claim or counterclaim initiated by or on behalf of such person. Such indemnification shall not be exclusive of other indemnification rights arising under any Bylaw, agreement, vote of directors or stockholders or otherwise and shall inure to the benefit of the heirs and legal representatives of such person. Any person seeking indemnification under this Article SEVENTH shall be deemed to have met the standard of conduct required for such indemnification unless the contrary shall be established. Any repeal or modification of the foregoing provisions of this Article SEVENTH shall not adversely affect any right or protection of a director or officer of this Corporation with respect to any acts or omissions of such director or officer occurring prior to such repeal or modification.

EIGHTH: The Corporation reserves the right at any time, and from time to time, to amend, alter, change or repeal any provision contained in this Second Amended and Restated Certificate of Incorporation, in a manner now or hereafter prescribed by the laws of the State of Delaware at the time in force, and all rights, preferences and privileges of whatsoever nature conferred upon stockholders, directors or any other persons whomsoever by and pursuant to this Second Amended and Restated Certificate of Incorporation in its present form or as hereafter amended are granted subject to the rights reserved in this Article EIGHTH.

[signature page follows]

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IN WITNESS WHEREOF, US ONCOLOGY HOLDINGS, INC. has caused this Second Amended and Restated Certificate of Incorporation to be signed by the undersigned authorized officers, who hereby acknowledges under penalties of perjury that the facts herein stated are true and that this certificate is his act and deed, this 21st day of December 2006.

US ONCOLOGY HOLDINGS, INC.
By:	/s/ R. DALE ROSS
	R. Dale Ross
	Chief Executive Officer

EX-10.1

Exhibit 10.1

EXECUTION COPY

STOCK PURCHASE AGREEMENT

US ONCOLOGY HOLDINGS, INC.

December 21, 2006

Table of Contents

Section 1.	Definitions	1
Section 2.	Sale of Series A-1 Preferred Stock and Common Stock; Use of Proceeds	6
2.1	Sale of Securities	6
2.2	Use of Proceeds	6
Section 3.	Closing Date; Delivery	6
3.1	Closing Date	7
3.2	Transactions to be Effected at the Closing	7
Section 4.	Representations and Warranties of the Company	8
4.1	Organization, Corporate Power and Licenses	8
4.2	Authorization	8
4.3	No Breach	8
4.4	Capital Stock and Related Matters	9
4.5	Subsidiaries; Investments	10
4.6	Financial Statements	11
4.7	Absence of Undisclosed Liabilities	11
4.8	No Material Adverse Change	11
4.9	Absence of Certain Developments	11
4.10	Assets	13
4.11	Real Property; Equipment, Fixtures and Inventory	13
4.12	Tax Matters	13
4.13	Contracts and Commitments	14
4.14	Intellectual Property Rights	16
4.15	Litigation, etc.	17
4.16	Brokerage	18
4.17	Consents	18
4.18	Insurance	18
4.19	Employees	18
4.20	ERISA	18
4.21	Compliance with Laws	19
4.22	Environmental and Safety Matters	19
4.23	Affiliated Transactions	21
4.24	Investment Company	21
4.25	Projections	21
4.26	SEC Filings	21
4.27	Securities Laws	21
4.28	Disclosure	21
Section 5.	Representations and Warranties of the Purchaser	22
5.1	Authority of Purchaser	22
5.2	Investment Representations	22
5.3	No Breach	23
Section 6.	Miscellaneous	23
6.1	Governing Law	23
6.2	Submission to Jurisdiction	23
6.3	Survival; Limitation on Liability	23
6.4	Successors and Assigns; No Third Party Beneficiaries	24

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6.5	Entire Agreement; No Reliance; Amendment	24
6.6	Notices	24
6.7	Expenses	25
6.8	Delays or Omissions	26
6.9	Severability of this Agreement	26
6.10	Titles and Subtitles	26
6.11	Counterparts	26
6.12	Gender	26
6.13	Public Announcement	26

EXHIBITS

Initial	Exhibit
A	Second Amended and Restated Certificate of Incorporation of the Company
B	Form of Amended and Restated Stockholders Agreement
C	Form of Amended and Restated Registration Rights Agreement
D	Form of Opinion of Company’s Counsel

DISCLOSURE SCHEDULE

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US ONCOLOGY HOLDINGS, INC.

STOCK PURCHASE AGREEMENT

STOCK PURCHASE AGREEMENT (the “Agreement”) dated as of the 21st day of December, 2006, by and among US Oncology Holdings, Inc., a Delaware corporation (the “Company”) and Morgan Stanley Strategic Investments, Inc. (the “Purchaser”).

THE PARTIES AGREE AS FOLLOWS:

Section 1. Definitions. For the purposes of this Agreement, the following terms have the meanings set forth below:

“Action” against a Person means an action, suit, litigation, arbitration, hearing, inquest, audit, examination or other proceeding against or affecting the Person or its property, whether civil, criminal, administrative, investigative or appellate, in law or equity before any mediator, arbitrator or Governmental Authority.

“Affiliate” of any particular Person means any other Person controlling, controlled by or under common control with such particular Person, where “control” means the possession, directly or indirectly, of the power to direct the management and policies of a Person whether through the ownership of voting securities, contract or otherwise; provided, that with respect to the Company, no Person which has entered into a management services agreement with the Company shall be considered an Affiliate of the Company solely because the Company provides management services to such Person.

“Affiliated Group” means any affiliated group as defined in IRC § 1504 that has filed a consolidated return for federal income tax purposes (or any similar group under state, local or foreign law) for a period during which the Company was a member.

“Ancillary Agreements” means collectively the Stockholders Agreement, the Registration Rights Agreement and the Side Letter.

“CERCLA” means the Comprehensive Environmental Response, Compensation and Liability Act of 1980, as amended from time to time, or any successor federal statute.

“CERCLIS” means the Comprehensive Environmental Response, Compensation and Liability Information System.

“Charter” has the meaning set forth in Section 3.2(a) hereof.

“Closing” has the meaning set forth in Section 3.1 hereof.

“Closing Date” has the meaning set forth in Section 3.1 hereof.

“Commercially Available Licenses” means any over-the-counter shrink wrap software or other non-negotiated comparable standard form licenses, other commercially available software program licenses or licenses for software embedded in equipment used by the Company or any of its Subsidiaries.

“Common Shares” has the meaning set forth in Section 2.1 hereof.

“Common Stock” means Common Stock of the Company, par value $0.001 per share.

“Environmental and Safety Laws” means any and all applicable present federal, state, local and foreign statutes, laws, regulations, ordinances and similar provisions having the force or effect of law, all judicial and administrative orders and determinations, all contractual obligations and common law concerning public health or safety, worker health or safety or pollution or protection of the environment, including, without limitation, those relating to any emissions, discharges or Releases of Hazardous Materials to ambient air, surface water, ground water or land, or otherwise relating to the manufacture, processing, distribution, use, treatment, storage, disposal, transport, control, cleanup or handling of Hazardous Materials.

“Environmental Permits” means all material permits, licenses and other authorizations which are required under Environmental and Safety Laws and applicable to the conduct of the Company’s business.

“Equity Security” of any Person means any capital stock or other ownership or equity interest or profit participation or similar right with respect to such Person (including any partnership or membership interest, any stock appreciation, phantom stock or similar right or plan, and any note or debt security having or containing equity or profit participation features), or any option, warrant or other security or right which is directly or indirectly convertible into or exercisable or exchangeable for any other Equity Security of such Person.

“Fully Diluted Basis” means “Fully Diluted Basis” as defined in the Stockholders Agreement.

“Governmental Authority” means any federal, state, municipal, national or other government, governmental department, commission, board, bureau, court, agency or instrumentality or political subdivision thereof or any entity or officer exercising executive, legislative, judicial, regulatory or administrative functions of any government or any court, in each case whether associated with a local government or state of the United States, the United States, or a foreign entity or government.

“Hazardous Material” means all or any of the following: (a) substances that are defined or listed in, or otherwise classified pursuant to, any applicable Environmental and Safety Laws as “hazardous substances” , “hazardous materials” , “hazardous wastes” , “toxic substances”, “medical waste”, “biological waste”, “infectious waste” or any other formulation intended to define, list or classify substances by reason of deleterious properties such as ignitability, corrosivity, reactivity, carcinogenicity, reproductive toxicity, “TLCP” toxicity or “EP” toxicity; (b) oil, petroleum or petroleum derived substances, natural gas, natural gas liquids or synthetic gas and drilling fluids, produced waters and wastes associated with the exploration, development or production of crude oil, natural gas or geothermal resources; (c) any flammable substances or explosives or

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any radioactive materials; (d) underground storage tanks, whether empty or containing any substance; (e) surface impoundments; (f) asbestos in any form; and (g) electrical or other equipment which contains any oil, lubricants, hydraulic fluid or dielectric fluid containing polychlorinated biphenyls.

“Indebtedness” means at a particular time, without duplication, (i) any indebtedness for borrowed money or issued in substitution for or exchange of indebtedness for borrowed money, (ii) any indebtedness evidenced by any note, bond, debenture or other debt security, (iii) any indebtedness for the deferred purchase price of property or services with respect to which a Person is liable, contingently or otherwise, as obligor or otherwise (other than trade payables and other current liabilities incurred in the ordinary course of business), (iv) any commitment by which a Person assures a creditor against loss (including, without limitation, contingent reimbursement obligations with respect to letters of credit), (v) any indebtedness guaranteed in any manner by a Person (including, without limitation, guarantees in the form of an agreement to repurchase or reimburse), (vi) any indebtedness secured by a Lien on a Person’s assets (other than Permitted Liens) and (vii) any unsatisfied obligation for “withdrawal liability” to a “multi-employer plan” as such terms are defined under ERISA (as defined in Section 4.20 hereof); provided that “Indebtedness” does not include the Shares or operating leases.

“Intellectual Property Rights” means all (i) patents, patent applications, patent disclosures and inventions, (ii) trademarks, service marks, trade dress, trade names, logos and corporate names and registrations and applications for registration thereof together with all of the goodwill associated therewith, (iii) copyrights (registered or unregistered) and copyrightable works and registrations and applications for registration thereof, (iv) mask works and registrations and applications for registration thereof, (v) computer software, data, data bases and documentation thereof, (vi) trade secrets and other confidential information (including, without limitation, ideas, formulas, compositions, inventions (whether patentable or unpatentable and whether or not reduced to practice), know how, manufacturing and production processes and techniques, research and development information, drawings, specifications, designs, plans, proposals, technical data, copyrightable works, financial and marketing plans and customer and supplier lists and information), and (vii) copies and tangible embodiments thereof (in whatever form or medium).

“Investment” as applied to any Person means (i) any loan made by such Person, (ii) any direct or indirect purchase or other acquisition by such Person of any notes, obligations, instruments, evidence of Indebtedness, stock, securities, ownership interest or Equity Interest (including partnership interests and joint venture interests) of any other Person and (iii) any capital contribution by such Person to any other Person, in each case other than investments in money market funds or similar short term non equity investments.

“IRC” means the Internal Revenue Code of 1986, as amended, and any reference to any particular IRC section shall be interpreted to include any revision of or successor to that section regardless of how numbered or classified. “IRS” means the United States Internal Revenue Service.

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“Latest Balance Sheet” means the unaudited consolidated balance sheet of the Company as of September 30, 2006.

“Lien” means (i) any mortgage, pledge, security interest, encumbrance, lien or charge of any kind (including, without limitation, any conditional sale or other title retention agreement or lease in the nature thereof), (ii) any sale of receivables with recourse against the Company, (iii) any filing or agreement to file a financing statement as debtor under the Uniform Commercial Code of the State of New York or any similar statute other than to reflect ownership by a third party of property leased to the Company under a lease which is not in the nature of a conditional sale or title retention agreement, or (iv) any subordination arrangement in favor of another Person (other than any subordination arising in the ordinary course of business).

“Loss” means any and all liabilities, obligations, losses, damages (but not, except in the case of fraud by the Company or any Person acting or purporting to act on the Company’s behalf, special, consequential or punitive damages or loss of future profits), diminution in value, interest, fines, settlements and reasonable and actually incurred attorneys’ fees, expenses, costs (including such costs for preparation and investigation) and disbursements. For avoidance of doubt, in determining Losses, the parties will take into account the impact of such items on the consolidated earnings and enterprise value of the Company and its Subsidiaries.

“Material Adverse Effect” means a material adverse effect on the business, operations, financial condition, operating results, assets or liabilities of Company and its Subsidiaries taken as a whole.

“Option” means any option to purchase Common Stock of the Company.

“Permitted Liens” means:

(i) tax liens with respect to taxes not yet due and payable or which are being contested in good faith by appropriate proceedings and for which appropriate reserves have been established in accordance with generally accepted accounting principles, consistently applied;

(ii) purchase money security interests in any property acquired by the Company;

(iii) trust deeds or mortgages on real property acquired by the Company;

(iv) interests or title of a lessor under any lease;

(v) mechanics’, materialmen’s or contractors’ liens or encumbrances or any similar lien or restriction for amounts not yet due and payable;

(vi) easements, rights of way, restrictions and other similar charges and encumbrances on real property not interfering with the ordinary conduct of the

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business of the Company or detracting from the value of the assets of the Company; and

(vii) such other liens, claims or encumbrances that are not material in amount and do not materially detract from the value of or materially impair the existing use of the property affected by such lien, claim or encumbrance.

“Person” means an individual, a partnership, a corporation, a limited liability company, an association, a joint stock company, a trust, a joint venture, an unincorporated organization and a Governmental Authority.

“Preferred Shares” has the meaning set forth in Section 2.1 hereof.

“RCRA” means the Resource Conservation and Recovery Act of 1976, as amended from time to time, or any successor federal statute.

“Registration Rights Agreement” means the Registration Rights Agreement dated the date hereof substantially in the form attached hereto as Exhibit C.

“Regulation” means each applicable law, rule, regulation or order by any Governmental Authority and each judgment, injunction, order, writ, decree or award of any Governmental Authority, arbitrator or other Person.

“Release” means any “release” as such term is defined in CERCLA, 42 U.S.C. § 9601(22), or any successor federal statute or analogous state law. For purposes of this Agreement, however, none of the exclusions (A) through (C) of 42 U.S.C. § 9601(22) apply.

“Securities Act” means the Securities Act of 1933, as amended, or any similar federal law then in force.

“Securities and Exchange Commission” means the United States Securities and Exchange Commission, including any governmental body or agency succeeding to the functions thereof.

“Securities Exchange Act” means the Securities Exchange Act of 1934, as amended, or any similar federal law then in force.

“Series A Preferred Stock” means Series A Participating Preferred Stock of the Company, par value $0.001 per share.

“Series A-1 Preferred Stock” means Series A-1 Participating Preferred Stock of the Company, par value $0.001 per share.

“Shares” has the meaning set forth in Section 2.1 hereof.

“Side Letter” means the Side Letter dated the date hereof among the Company, WCAS and the Purchaser.

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“Stockholders Agreement” means the Stockholders Agreement dated the date hereof substantially in the form attached hereto as Exhibit B.

“Subsidiary” means, with respect to the Company, any corporation, partnership, limited liability company, association, joint venture or other business entity of which more than 50% of the total voting power, shares of stock or other ownership interests entitled (without regard to the occurrence of any contingency) to vote in the election of Persons (whether directors, managers, trustees or other Persons performing similar functions) having the power to direct or cause the direction of the management and policies thereof is at the time owned or controlled, directly or indirectly, by the Company or one or more of the other Subsidiaries of the Company or a combination thereof.

“Tax” or “Taxes” means federal, state, county, local, foreign or other income, gross receipts, ad valorem, franchise, profits, sales or use, transfer, registration, excise, utility, environmental, communications, real or personal property, capital stock, license, payroll, wage or other withholding, employment, social security, severance, stamp, occupation, alternative or add on minimum, estimated and other taxes of any kind whatsoever (including, without limitation, deficiencies, penalties, additions to tax, and interest attributable thereto) whether disputed or not.

“Tax Return” means any return, information report or filing with respect to Taxes, including any schedules attached thereto and including any amendment thereof.

“WCAS” means Welsh, Carson, Anderson & Stowe IX, L.P.

References to the “knowledge” of the Company or of any Subsidiary means the knowledge, after reasonable inquiry, of the general counsel or any director or executive officer of the Company and its Subsidiaries.

Section 2. Sale of Series A-1 Preferred Stock and Common Stock; Use of Proceeds.

2.1 Sale of Securities. Subject to the terms and conditions hereof, on the Closing Date (as defined in Section 3.1) the Company will issue and sell to the Purchaser, and the Purchaser will purchase from the Company, an aggregate of 1,948,251 shares of Series A-1 Preferred Stock (the “Preferred Shares”) and 21,649,849 shares of Common Stock (the “Common Shares” and together with the Preferred Shares, the “Shares”), at a purchase price of approximately $26.03 per share of Series A-1 Preferred Stock and approximately $4.59 per share of Common Stock for an aggregate purchase price of One Hundred Fifty Million Dollars ($150,000,000) (the “Purchase Price”).

2.2 Use of Proceeds. The net proceeds from the sale of the Shares, together with existing cash on hand, shall be used by the Company to pay a one-time dividend (the “Dividend”) of up to One Hundred and Ninety Million Dollars ($190,000,000), in the aggregate, to the holders of capital stock of the Company (other than the Purchaser) and to pay the fees and expenses related to the transactions contemplated hereby (not to exceed One Million Dollars ($1,000,000) in total).

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Section 3. Closing Date; Delivery.

3.1 Closing Date. The closing of the purchase and sale of the Shares (the “Closing”) shall be held at the offices of Richards Kibbe & Orbe LLP, One World Financial Center, New York, New York 10281, at 12:00 p.m., on December 21, 2006, or at such other time and place to which the Company and the Purchaser may agree (the “Closing Date”).

3.2 Transactions to be Effected at the Closing. Upon the terms and subject to the conditions of this Agreement, at the Closing, the parties will make the deliveries set forth in this Section 3.2.

(a) Company Deliveries. The Company will deliver to the Purchaser:

(i) a copy of the Amended and Restated Certificate of Incorporation in the form set forth in Exhibit A (the “Charter”), certified by the Secretary of State of the State of Delaware as filed and effective;

(ii) the share certificates representing the Shares, registered in the names of the Purchaser, duly executed and delivered by the Company;

(iii) a copy of each of the Ancillary Agreements, duly executed and delivered by all parties thereto other than the Purchaser;

(iv) a legal opinion from counsel to the Company addressed to the Purchaser, dated the Closing Date, substantially in the form of Exhibit D attached hereto;

(v) a certificate, executed by the Secretary of the Company, dated the Closing Date, attaching (i) the Charter, certified by the Secretary of State of the State of Delaware as filed and effective, (ii) the bylaws of the Company, (iii) duly adopted resolutions of the Board of Directors and shareholders of the Company authorizing the Company to consummate all of the transactions contemplated hereby (including, without limitation, the issuance of the Shares and issuance of the Common Stock upon conversion of the Preferred Shares), (iv) the names and true signatures of the officers of the Company authorized to sign this Agreement and the Ancillary Agreements and (v) a certificate of good standing from the Secretary of State of the State of Delaware dated a recent date prior to the Closing Date for each of the Company and US Oncology, Inc.;

(vi) a certificate, executed by the Chief Executive Officer of the Company, dated the Closing Date, certifying that the representations and warranties made by the Company in Section 4 shall be true and correct in all respects on the Closing Date and that the Company shall have performed all obligations and conditions herein required to be performed by it on or prior to the Closing Date;

(vii) copies of all permits, consents, approvals, authorizations, declarations and filings set forth on Schedule 4.4 and Schedule 4.17; and

(viii) such other documents as the Purchaser or its counsel may reasonably request to demonstrate satisfaction of the conditions and compliance with the agreements set forth in this Agreement and the Ancillary Agreements.

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(b) Purchaser Deliveries. The Purchaser will deliver to the Company:

(i) the Purchase Price, by wire transfer of immediately available funds; and

(ii) a copy of each of the Ancillary Agreements, duly executed and delivered by the Purchaser.

Section 4. Representations and Warranties of the Company. Contemporaneously with the execution and delivery of this Agreement, the Company is delivering to the Purchaser a disclosure schedule with numbered schedules corresponding to the relevant sections or subsections in this Agreement (the “Disclosure Schedule”). Nothing in the Disclosure Schedule is intended to broaden the scope of any representation or warranty of the Company contained in this Agreement. The inclusion of any information in the Disclosure Schedule shall not be deemed to be an admission or acknowledgement, in and of itself, that such information is material, has resulted in or would result in a Material Adverse Effect or is outside the ordinary scope of business. The Company hereby represents and warrants to the Purchaser that:

4.1 Organization, Corporate Power and Licenses. The Company and each Subsidiary is duly organized, validly existing and in good standing under the laws of the jurisdiction of its organization and is duly qualified to do business in every jurisdiction in which its ownership of property or conduct of business requires it to qualify, except to the extent that the failure to be so qualified would not reasonably be expected to, individually or in the aggregate, result in a Material Adverse Effect. The Company and each Subsidiary possesses all requisite corporate or other power and authority and all material licenses, permits and authorizations necessary to own and operate its properties, to carry on its business as now conducted and presently proposed to be conducted, to execute and deliver this Agreement and the Ancillary Agreements and to carry out the transactions contemplated by this Agreement and to undertake their obligations contemplated by the Ancillary Agreements. The Company’s Charter (a copy of which is attached hereto as Exhibit A) and bylaws (a copy of which has been furnished to the Purchaser) reflect all amendments made thereto at any time prior to the date of this Agreement and are correct and complete and are in full force and effect.

4.2 Authorization. The execution, delivery and performance by the Company of this Agreement and the Ancillary Agreements has been duly authorized by the Company. This Agreement and each Ancillary Agreement constitutes (assuming due execution by the other party or parties thereto), a valid and binding obligation of the Company, enforceable in accordance with its terms, except as enforcement may be limited by applicable bankruptcy laws or other similar laws affecting creditors’ rights generally, and except insofar as the availability of equitable remedies may be limited by applicable law from time to time.

4.3 No Breach. The execution and delivery by the Company of this Agreement and the Ancillary Agreements, the offering, sale and issuance of the Shares hereunder, the issuance of the Common Stock upon conversion of the Preferred Shares, the payment of the Dividend and the fulfillment of and compliance with the respective terms hereof and thereof by the Company, do not and will not (i) conflict with or result in a breach of the terms, conditions or provisions of, (ii) constitute a default under, (iii) result in the creation of any Lien upon the Company’s capital stock or assets pursuant to, (iv) give any third party the right to modify, terminate or accelerate any obligation under, (v) result in a violation of, or (vi) require any authorization, consent, approval, exemption or other action by or notice or declaration to, or filing with, any Governmental Authority pursuant to, the charter or bylaws of the Company, or

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any law, statute, rule or regulation to which the Company or any Subsidiary is subject, or any agreement, instrument, order, judgment or decree to which the Company or any Subsidiary is subject, except, (A) for any such permit, consent, approval, authorization, declaration or filing set forth on Schedule 4.17, each of which shall have been obtained on or prior to the Closing Date and (B) in the case of any of any agreement or instrument to which the Company is subject, for such authorizations, consents or approvals that, if not so obtained, would not reasonably be expected to, individually or in the aggregate, result in a Material Adverse Effect.

4.4 Capital Stock and Related Matters. Except as set forth on Schedule 4.4:

(a) On the date hereof and prior to giving effect to the transactions contemplated by this Agreement, (i) the authorized and issued capital stock of the Company consists solely of 17,000,000 shares of Participating Preferred Stock, $0.001 par value per share (“Participating Preferred Stock”), consisting of the Series A Preferred Stock and the Series A-1 Preferred Stock, of which 13,938,657 shares of Series A Preferred Stock are issued and outstanding and no shares of Series A-1 Preferred Stock are issued and outstanding, and 300,000,000 shares of Common Stock, of which 119,372,031 shares are issued and outstanding, (ii) Options to purchase 3,622,500 shares of Common Stock have been issued and (iii) 13,938,657 shares of Common Stock are reserved for issuance upon conversion of the outstanding shares of Series A Preferred Stock and 3,622,500 shares of Common Stock are reserved for issuance upon conversion of the Options. Schedule 4.4 sets forth the number of issued and outstanding shares of Series A Preferred Stock, Series A-1 Preferred Stock and Common Stock, the names of the record owners thereof and the number of shares of Series A Preferred Stock, Series A-1 Preferred Stock and Common Stock held by each such owner. Schedule 4.4 also sets forth the number of issued and outstanding Options, the number of shares of Common Stock for which the Options may be exercised, the exercise prices, the expiration dates and the names of the record owners thereof.

(b) As of the Closing and immediately after giving effect to the transactions contemplated hereby, (w) (i) the authorized and issued capital stock of the Company consists solely of 17,000,000 shares of Participating Preferred Stock, of which 13,938,657 shares of Series A Preferred Stock are issued and outstanding and 1,948,251 shares of Series A-1 Preferred Stock are issued and outstanding, and 300,000,000 shares of Common Stock, of which 141,021,880 shares are issued and outstanding, (ii) Options to purchase 3,622,500 shares of Common Stock have been issued and (iii) 15,886,908 shares of Common Stock are reserved for issuance upon conversion of the outstanding shares of Series A Preferred Stock and Series A-1 Preferred Stock and 3,622,500 shares of Common Stock are reserved for issuance upon conversion of the Options, (x) the Company shall not be subject to any obligation (contingent or otherwise) to repurchase or otherwise acquire or retire any of its Equity Securities, except as contemplated by the Charter upon the occurrence of certain events (none of which have yet occurred), (y) the Company shall not have outstanding any Equity Securities, except as set forth in this Section 4.4(b) and (z) all of the outstanding shares of the Company’s capital stock identified above shall be validly issued, fully paid and nonassessable.

(c) There are no statutory or contractual shareholders preemptive rights or rights of refusal with respect to (i) the issuance of the Shares hereunder or the issuance of the Common Stock upon conversion of the Preferred Shares or (ii) the

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issuance by the Company of any other Equity Security, other than any such rights listed on Schedule 4.4, each of which have been waived prior to the date hereof. The Company has not violated any applicable federal or state securities laws in connection with the offer, sale or issuance of any of its capital stock, and the offer, sale and issuance of the Shares hereunder do not require registration under the Securities Act or any applicable state securities laws. There are no agreements between the Company’s shareholders or between any of the Company’s shareholders and the Company, with respect to the voting or transfer of the Company’s capital stock, with respect to the issuance, purchase, redemption or sale of any Equity Security or with respect to any other aspect of the Company’s affairs other than the Stockholders Agreement or as set forth on Schedule 4.4.

(d) The Shares purchased by the Purchaser hereunder will have the terms and provisions set forth in the Charter. Upon delivery to the Purchaser at the Closing of the share certificates with respect to the Shares, (i) the Purchaser will become the sole record legal and beneficial owner of such Shares and good and marketable title to such Shares will pass to the Purchasers, free and clear of any Liens, options, charges and transfer restrictions of any kind, except for those created by this Agreement, the Ancillary Agreements and applicable securities laws, and (ii) such Shares will be duly authorized, validly issued, fully paid and nonassessable. Upon the conversion of the Preferred Shares as provided in the Charter, (A) the Purchaser will become the sole record legal and beneficial owner of the shares of Common Stock issuable upon such conversion and good and marketable title to such shares of Common Stock will pass to the Purchaser, free and clear of any Liens, options, charges and transfer restrictions of any kind, except for those created by this Agreement, the Ancillary Agreements and applicable securities laws, and (B) such shares of Common Stock will be duly authorized, validly issued, fully paid and nonassessable. The Company currently has, and at all times will maintain, a sufficient number of authorized but unissued shares of Common Stock so that the Company will at all times have a sufficient number of authorized shares of Common Stock to issue upon the conversion in full of all of the Preferred Shares.

(e) As of the Closing Date, (i) the “Accreted Value” (as defined in the Charter) with respect to each share of Series A Preferred Stock issued on August 20, 2004 is $21.4475, (ii) the “Unpaid Base Amount” (as defined in the Charter) with respect to each such share of Series A Preferred Stock is $19.01, (iii) the sum of all unpaid amounts previously declared in respect of each such share of Series A Preferred Stock as “Special Dividends” (as defined in the Charter) is $0 and (iv) the “Conversion Value” (as defined in the Charter) in respect of each such share of Series A Preferred Stock is $21.4475.

(f) Other than as contemplated by Section 2.2 above, there are no declared and unpaid dividends on either the Series A Preferred Stock or the Common Stock.

4.5 Subsidiaries; Investments. Except as set forth on Schedule 4.5, the Company does not own or hold any (a) interest in and does not control, directly or indirectly, any Subsidiary or (b) any Equity Securities, or the right to acquire any Equity Securities, of any other Person. Each of the Equity Securities of each Subsidiary is owned of record, free and clear of any Liens, by the Persons set forth on Schedule 4.5.

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4.6 Financial Statements. The Company has previously filed with the Securities and Exchange Commission the following financial statements:

(a) the audited consolidated balance sheets of the Company as of December 31, 2004 and December 31, 2005 and the related statements of income and cash flows (or the equivalent) for the fiscal years then ended, respectively; and

(b) the Latest Balance Sheet, and the related statement of income (or the equivalent) for the nine month period then ended.

Each of the foregoing financial statements (including in all cases the notes thereto, if any), along with the unaudited consolidated balance sheet of the Company as of November 30, 2006 and the related unaudited statement of income (or the equivalent) for the eleven month period ended November 30, 2006, has been prepared in accordance with generally accepted accounting principles, consistently applied, subject in the case of the unaudited financial statements to the absence of footnote disclosure and changes resulting from normal year end adjustments (none of which would, alone or in the aggregate, reasonably be expected to be materially adverse to the financial condition, operating results, assets or operations of the Company) and fairly present, in all material respects, the financial position of the Company and its Subsidiaries as of their respective dates.

4.7 Absence of Undisclosed Liabilities. Except as set forth on Schedule 4.7, neither the Company nor its Subsidiaries has or will have as of the Closing any obligation or liability (whether accrued, absolute, contingent, unliquidated or otherwise, whether or not known to the Company, whether due or to become due and regardless of when asserted) arising out of transactions entered into at or prior to the date of this Agreement, or any action or inaction at or prior to the date of this Agreement, or any state of facts existing at or prior to the date of this Agreement other than: (i) as reflected in the Latest Balance Sheet, (ii) liabilities and obligations which have arisen after the date of the Latest Balance Sheet in the ordinary course of business (none of which is a material liability resulting from breach of contract, breach of warranty, tort, infringement claim or lawsuit), and (iii) liabilities which individually or in the aggregate do not and could not reasonably be expected to have a Material Adverse Effect.

4.8 No Material Adverse Change. Except as set forth on Schedule 4.8, since September 30, 2006, there has been no Material Adverse Effect.

4.9 Absence of Certain Developments. Except as expressly contemplated by this Agreement or as set forth on Schedule 4.9, since September 30, 2006, neither the Company nor any Subsidiary has:

(a) issued any notes, bonds or other debt securities or instruments or any capital stock or other Equity Securities;

(b) borrowed any amount, guaranteed any obligation of any Person or incurred or become subject to any Indebtedness or other material liabilities, except current liabilities incurred in the ordinary course of business and liabilities under contracts entered into in the ordinary course of business;

(c) discharged or satisfied any Lien or paid any obligation or liability, other than current liabilities paid in the ordinary course of business;

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(d) mortgaged or pledged any of its properties or assets or subjected them to any Lien, except Permitted Liens;

(e) sold, assigned or transferred any of its assets with a book value or fair market value in excess of $1,000,000 in the aggregate, except inventory or obsolete or replaced equipment disposed of in the ordinary course of business, or canceled any debts or claims;

(f) sold, assigned or transferred any Intellectual Property Rights, or disclosed any proprietary confidential information to any Person (other than the Purchaser or any representative thereof);

(g) suffered any extraordinary losses or waived any material rights of value, whether or not in the ordinary course of business or consistent with past practice;

(h) made capital expenditures or commitments therefor that aggregate in excess of $5,000,000;

(i) made any loans or advances to, guarantees for the benefit of, any Persons in excess of $1,000,000 in the aggregate, other than guarantees of trade payables of the Company’s Subsidiaries made in the ordinary course of business consistent with past practices;

(j) made or acquired any Investment in any Person individually or in the aggregate in excess of $1,000,000;

(k) made any charitable contributions or pledges in excess of $250,000 in the aggregate;

(l) suffered any damage, destruction or casualty loss exceeding in the aggregate $500,000 whether or not covered by insurance;

(m) declared or made any payment or distribution of cash or other property to its shareholders with respect to its Equity Securities or purchased or redeemed any of its Equity Securities;

(n) merged, consolidated with, or entered into any business combination with any Person, or sold all or substantially all of its assets to any other Person;

(o) entered into any material contract or transaction with any of its Affiliates (other than WCAS and its Affiliates) or entered into any contract or transaction with WCAS and its Affiliates (other than any Ancillary Agreement);

(p) paid or agreed to pay any bonus, extra compensation, pension or severance pay, or otherwise increased the wage, salary or compensation (of any nature) to any of its directors or executive officers other than in the ordinary course of business consistent with past practices;

(q) entered into any other material transaction not in the ordinary course of business; or

(r) committed or agreed to do any of the foregoing.

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4.10 Assets. Except as set forth on Schedule 4.10, the Company and each Subsidiary has good and marketable title to, or a valid leasehold interest in, the properties and tangible assets used in and material to its business and reflected in the financial statements referred to in Section 4.6, free and clear of all Liens, except for (i) inventory and obsolete or replaced equipment disposed of in the ordinary course of business since the date of the Latest Balance Sheet, (ii) Liens securing Indebtedness reflected in the Latest Balance Sheet (or notes related thereto) and (iii) Permitted Liens. Except as set forth on Schedule 4.10, the Company’s and each Subsidiary’s buildings, equipment and other tangible assets used in and material to its business are in good operating condition in all material respects (ordinary wear and tear excepted) and are fit for use in the ordinary course of business.

4.11 Real Property; Equipment, Fixtures and Inventory.

(a) The Company or one of its Subsidiaries, as the case may be, has good and marketable title in fee simple, or good and marketable leasehold interest in, all of the real property used in and material to its business (“Real Property”), free and clear of all Liens, except Liens securing Indebtedness reflected in the Latest Balance Sheet (or notes related thereto) and Permitted Liens. The Company and its Subsidiaries enjoy peaceful and undisturbed possession of all leased Real Property.

(b) No instrument of record, easement, license, use restriction, grant or applicable zoning, building or urban redevelopment Regulation or other impediment of any kind prohibits in any material respect, or materially interferes with, limits or impairs the use, operation, maintenance of, or access to, or materially affects the value of, the Real Property or any item of personal property related to the Real Property.

4.12 Tax Matters. Except as set forth on Schedule 4.12:

(a) The Company, and each Affiliated Group have filed all Tax Returns which they are required to file under applicable laws and regulations; all such Tax Returns are complete and correct in all material respects and have been prepared in compliance with all applicable laws and regulations in all material respects; the Company and each Affiliated Group in all material respects have paid all Taxes due and owing by them (whether or not such Taxes are required to be shown on a Tax Return) and have withheld and paid over to the appropriate taxing authority all Taxes which they are required to withhold from amounts paid or owing to any employee, stockholder, creditor or other third party; neither the Company nor any Affiliated Group has waived any statute of limitations with respect to any material Taxes or agreed to any extension of time with respect to any material Tax assessment or deficiency; the accrual for Taxes on the Latest Balance Sheet would be adequate to pay all Tax liabilities of the Company if its current tax year were treated as ending on the date of the Latest Balance Sheet (excluding any amount recorded which is attributable solely to timing differences between book and Tax income); since the date of the Latest Balance Sheet, the Company has not incurred any liability for Taxes other than in the ordinary course of business; the assessment of any additional Taxes for periods for which Tax Returns have been filed by the Company and each Affiliated Group shall not exceed the recorded liability therefore on the Latest Balance Sheet (excluding any amount recorded which is attributable solely to timing differences between book and Tax income); no foreign, federal, state or local tax audits or administrative or judicial proceedings are pending or being conducted with respect to

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the Company or any Affiliated Group, no information related to Tax matters has been requested by any foreign, federal, state or local taxing authority and no written notice indicating an intent to open an audit or other review has been received by the Company from any foreign, federal, state or local taxing authority; and there are no material unresolved questions or claims concerning the Company’s or any Affiliated Group Tax liability.

(b) The Company has not made an election under IRC §341(f). The Company is not liable for the Taxes of another Person in a material amount under (a) Treas. Reg. §1.1502-6 (or comparable provisions of state, local or foreign law), (b) as a transferee or successor, (c) by contract or indemnity or (d) otherwise. The Company is not a party to any tax sharing agreement. The Company and each Affiliated Group have disclosed on their federal income Tax Returns any position taken for which substantial authority (within the meaning of IRC §6662(d)(2)(B)(i)) did not exist at the time the return was filed. The Company has not made any payments, is not obligated to make payments or is not a party to an agreement that could obligate it to make any payments that would not be deductible under IRC §280G.

(c) The Company is not a “United States real property holding corporation”, as defined in IRC §897 and in applicable regulations thereunder.

4.13 Contracts and Commitments.

(a) Except for this Agreement and the Ancillary Agreements or as set forth on Schedule 4.13, neither the Company nor any Subsidiary is a party to or bound by any written or oral:

(i) pension, profit sharing, stock option, employee stock purchase or other plan or arrangement providing for deferred or other compensation to employees or any other employee benefit plan or arrangement, or any collective bargaining agreement or any other contract with any labor union, or any severance agreement, program, policy or arrangement;

(ii) contract for the employment of any officer, individual employee or other Person on a full time, part time, consulting or other basis providing annual compensation in excess of $250,000 or contract relating to loans to officers, directors or Affiliates;

(iii) retainer or consulting contracts for which the aggregate amounts required to be paid under each such contract does not exceed $500,000;

(iv) contract under which the Company or any Subsidiary has advanced or loaned any other Person amounts in the aggregate exceeding $1,000,000.

(v) contracts with respect to any Investment in any other Person, other than acquisitions of affiliated physician practices in the ordinary course of business;

(vi) agreement or indenture relating to Indebtedness or the mortgaging, pledging or otherwise placing a Lien on any material asset or material group of assets of the Company or any Subsidiary;

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(vii) guarantee of any obligation of another Person for an amount individually or in the aggregate in excess of $1,000,000;

(viii) lease or agreement under which the Company or any Subsidiary is lessee of or holds or operates any property, real or personal, owned by any other party, except for any lease of real or personal property under which the aggregate annual rental payments do not exceed $1,000,000;

(ix) lease or agreement under which the Company or any Subsidiary is lessor of or permits any third party to hold or operate any property, real or personal, owned or controlled by the Company or such Subsidiary;

(x) contract or group of related contracts with the same party or group of affiliated parties the performance of which involves future consideration in excess of $1,000,000, provided that purchases of inventory in the ordinary course of business consistent with past practices and sales invoices are not required to be listed;

(xi) assignment, license, indemnification or agreement with respect to any intangible property material to the operation of the Company’s or any Subsidiary’s business (including, without limitation, any Intellectual Property Right, but excluding any Commercially Available Licenses);

(xii) agreement with any federal, state or local government or subdivision, agency or authority thereof;

(xiii) agreement under which it has granted any Person any registration rights (including, without limitation, demand and piggyback registration rights);

(xiv) sales, distribution or franchise agreement, or other agreements material to the operation of the Company’s or any Subsidiary’s business with a term of more than six months which is not terminable by the Company or such Subsidiary upon less than 90 days notice without penalty;

(xv) contract or agreement with respect to any merger, consolidation with, or entrance into any business combination with any Person, or sale of all or substantially all of its assets to any other Person;

(xvi) material contract or agreement with any of its Affiliates (other than WCAS and its Affiliates) or any contract or agreement with WCAS and its Affiliates;

(xvii) non-competition, non-disclosure or other contract or agreement restricting the conduct of business of (A) the Company in any material respect or (B) any shareholders of the Company; or

(xviii) any other agreement which is material to its operations and business prospects and is required to be filed by the Company with the Securities and Exchange Commission.

(b) All of the contracts, agreements and instruments set forth or required to be set forth on Schedule 4.13 (collectively, the “Material Contracts”) are

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valid, binding and enforceable in accordance with their respective terms. Except as, individually or in the aggregate, would not reasonably be expect to have a Material Adverse Effect, the Company and each Subsidiary has performed all obligations required to be performed by it, is not in default under or in breach of nor in receipt of any claim of default or breach under any Material Contract, and no event has occurred which with the passage of time or the giving of notice or both would result in a default, breach or event of noncompliance by the Company or any Subsidiary under any Material Contract. Neither the Company nor any Subsidiary has present expectation or intention of not fully performing all material obligations under the Material Contracts; and the Company has no knowledge of any breach or anticipated breach by the other parties to any Material Contract in any material respect.

(c) Prior to the date of this Agreement, the Company has furnished to the Purchaser correct and complete copies of all Material Contracts.

4.14 Intellectual Property Rights.

(a) Schedule 4.14 contains a complete and accurate list of all (a) registered Intellectual Property Rights owned by the Company and its Subsidiaries, (b) pending applications for registrations of Intellectual Property Rights filed by the Company and its Subsidiaries, (c) material unregistered trade names and corporate names owned or used by the Company and its Subsidiaries and (d) material unregistered trademarks, service marks, copyrights, mask works and computer software (other than commercially available software) owned or used by the Company and its Subsidiaries. Schedule 4.14 also contains a complete and accurate list of all material licenses and other rights granted by the Company and its Subsidiaries to any third party with respect to any Intellectual Property Rights and all material licenses and other rights granted by any third party to the Company and its Subsidiaries with respect to any Intellectual Property Rights (other than Commercially Available Licenses), in each case identifying the subject Intellectual Property Rights. The Company and its Subsidiaries owns all right, title and interest to, have the right to use pursuant to a valid license, or is otherwise free to use all Intellectual Property Rights necessary for the operation of the businesses of the Company and its Subsidiaries as presently conducted and as presently proposed to be conducted, free and clear of all Liens, except as, individually or in the aggregate, would not reasonably be expect to have a Material Adverse Effect (the “Required Intellectual Property”). No loss or expiration of any Intellectual Property Right or related group of Intellectual Property Rights owned or used by the Company and its Subsidiaries or any which would reasonably be expected to have a material adverse effect on the conduct of the Company’s business is, to the best of the Company’s knowledge, threatened, pending or reasonably foreseeable. The Company and its Subsidiaries have taken all reasonably necessary actions to maintain and protect the Required Intellectual Property Rights which it or they own. To the best of the Company’s knowledge, the owners of any Required Intellectual Property Rights licensed to the Company and its Subsidiaries have taken all reasonably necessary actions to maintain and protect the Intellectual Property Rights which are subject to such licenses.

(b) Except as set forth on Schedule 4.14, (a) the Company and its Subsidiaries own all right, title and interest in and to all of the Intellectual Property Rights listed as owned on such schedule, free and clear of all Liens, (b) there have been

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no claims made against the Company or any Subsidiary asserting the invalidity, misuse or unenforceability of any of such Intellectual Property Rights, and, to the Company’s knowledge, there are no grounds for the same, (c) neither the Company nor any Subsidiary has received any notices of, or is aware of any facts which indicate a likelihood of, any infringement or misappropriation by, or conflict with, any third party with respect to such Intellectual Property Rights (including, without limitation, any demand or request that the Company license any rights from a third party), (d) the conduct of the Company’s or any Subsidiary’s business has not infringed, misappropriated or conflicted with and does not infringe, misappropriate or conflict with any Intellectual Property Rights of other Persons in any material respect, nor would any future conduct as presently contemplated infringe, misappropriate or conflict with any Intellectual Property Rights of other Persons in any material respect, and (e) to the best of the Company’s knowledge, the Intellectual Property Rights owned by or exclusively licensed to the Company and its Subsidiaries has not been infringed or misappropriated by other Persons.

(c) The transactions contemplated by this Agreement shall not have a material adverse effect on the Company’s or any Subsidiary’s right, title and interest in and to the Intellectual Property Rights listed on Schedule 4.14.

(d) The Required Intellectual Property owned by the Company and its Subsidiaries or as required by any licenses has been maintained in confidence in accordance with reasonable protection procedures and, to the extent that any portion of the Required Intellectual Property would otherwise qualify as a “trade secret”, which would be necessary to preserve its status as trade secrets under applicable Regulations. Except as set forth on Schedule 4.14, neither the Company nor any of its Subsidiaries has disclosed, released or authorized the disclosure or release of any proprietary or confidential Required Intellectual Property owned or used by the Company or one of its Subsidiaries in such a way as to relinquish the proprietary or confidential status of the Required Intellectual Property.

(e) All former and current employees, agents, consultants and independent contractors of the Company and its Subsidiaries who have contributed to or participated in, in any material respect, the conception and development of any of the Required Intellectual Property (collectively, “Personnel”), have executed and delivered to the Company or one of its Subsidiaries a proprietary information agreement restricting such Person’s right to disclose proprietary information of the Company and its Subsidiaries.

4.15 Litigation, etc. Except as set forth on Schedule 4.15, there are no Actions pending or, to the Company’s knowledge, threatened against the Company or any Subsidiary (or to the Company’s knowledge, pending or threatened against any of the officers, directors or employees of the Company or any Subsidiary with respect to its business or proposed business activities) (including, without limitation, any Actions with respect to the transactions contemplated by this Agreement). Except as specified on Schedule 4.15, none of such Actions listed or required to be listed on Schedule 4.15, if decided adversely to the Company or any Subsidiary, would reasonably be expected to have a Material Adverse Effect. Except as set forth on Schedule 4.15, neither the Company nor any Subsidiary is subject, to the Company’s knowledge, to any governmental investigations or inquiries (including, without limitation,

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inquiries as to the qualification to hold or receive any material license or permit). Neither the Company nor any Subsidiary is named in and subject to any judgment, order or decree of any Governmental Authority.

4.16 Brokerage. The Company has not engaged or employed any finder, broker, agent or other intermediary in connection with the transactions contemplated by this Agreement or the Ancillary Agreements. There are and will be no claims for brokerage commissions, finders’ fees or similar compensation in connection with the transactions contemplated by this Agreement or the Ancillary Agreements based on any arrangement or agreement entered into by or binding upon the Company.

4.17 Consents. Except as set forth on Schedule 4.17, no permit, consent, approval or authorization of, or declaration to or filing with, any Governmental Authority or any other Person is required in connection with the execution, delivery and performance by the Company of this Agreement, the Ancillary Agreements, or the consummation by the Company of any of the transactions contemplated hereby, including without limitation the offering, sale and issuance of the Shares hereunder, the issuance of the Common Stock upon conversion of the Preferred Shares and the payment of the Dividend. Each permit, consent, approval, authorization, declaration or filing listed on Schedule 4.17 will be obtained on or prior to the Closing Date.

4.18 Insurance. The Company and its Subsidiaries are covered by valid and currently effective insurance policies or binders of insurance, including general liability insurance, property insurance, workers’ compensation insurance and business interruption insurance, issued in favor of the Company or one of its Subsidiaries, in each case, with financially sound and reputable insurance companies and in such types and amounts and covering such risks as are reasonable and appropriate for the businesses and operations engaged in by the Company and its Subsidiaries. Neither the Company nor any of its Subsidiaries is in default with respect to its material obligations under any insurance policy maintained by any of them. The Company and its Subsidiaries do not have any self insurance or coinsurance programs.

4.19 Employees. The Company has no knowledge that any executive officer or other key employee of the Company or its Subsidiaries or any group of employees of the Company or its Subsidiaries has any plans to terminate employment with the Company or its Subsidiaries. The Company and its Subsidiaries have complied in all material respects with all laws relating to the employment of labor (including, without limitation, provisions thereof relating to wages, hours, equal opportunity, collective bargaining and the payment of social security and other taxes), and the Company has no knowledge that it has any material labor relations problems (including, without limitation, any union organization activities, threatened or actual strikes or work stoppages or material grievances). To the Company’s knowledge, none of the Company’s or any Subsidiary’s employees is subject to any noncompete, nondisclosure, confidentiality, employment, consulting or similar agreements relating to, affecting or in conflict with the present or proposed business activities of the Company or such Subsidiary, except for agreements between the Company or such Subsidiary and its present and former employees.

4.20 ERISA. Except as set forth on Schedule 4.20:

(a) Multiemployer Plans. The Company does not have any obligation to contribute to (or any other liability, including current or potential withdrawal liability,

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with respect to) any “multiemployer plan” (as defined in Section 3(37) of the Employee Retirement Income Security Act of 1974, as amended (“ERISA”)).

(b) Retiree Welfare Plans. The Company does not maintain or have any obligation to contribute to (or any other liability with respect to) any plan or arrangement whether or not terminated, which provides medical, health, life insurance or other welfare type benefits for current or future retired or terminated employees (except for continued benefit coverage required to be provided under Section 4980B of the IRC or as required under applicable state law), the liability for which has not been properly reflected on the Company’s financial statements.

(c) Defined Benefit Plans. The Company does not maintain, contribute to or have any liability under (or with respect to) any employee plan which is a “defined benefit plan” (as defined in Section 3(35) of ERISA) subject to Title IV of ERISA, whether or not terminated.

(d) Plan Compliance. With respect to each employee benefit plan or arrangement maintained by the Company (each, an “Employee Benefit Program”), the terms and operation of each such Employee Benefit Program comply and have heretofore complied in all material respects with all applicable laws and regulations relating to each such Employee Benefit Program. The Company has not incurred, nor has any event occurred nor does any circumstance exist that could reasonably be expected to result in the Company’s incurring, any material liability or excise tax with respect to any employee benefit, plan or program under Section 409 or Section 502 of ERISA or Chapter 43 of the Code with respect to any employee benefit plan, program or arrangement. No litigation, arbitration or governmental administrative proceeding (or investigation) or other proceeding (other than those relating to routine claims for benefits) is pending or, to the knowledge of the Company, threatened with respect to any Employee Benefit Program.

(e) The Company. For purposes of this Section 4.20, the term “Company” includes all organizations under common control with the Company pursuant to Section 4.14(b) or (c) of the IRC.

4.21 Compliance with Laws. Neither the Company nor any Subsidiary has violated any Regulation which violation has had or would reasonably be expected to have a Material Adverse Effect, and neither the Company nor any Subsidiary has received notice of any such violation. The Company and each Subsidiary is in compliance in all material respects with the USA Patriot Act (Title III of Pub.L. 107-56 (signed into law October 26, 2001)). No part of the proceeds hereunder will be used, directly or indirectly, for any payments to any governmental official or employee, political party, official of a political party, candidate for political office or anyone else acting in an official capacity, in order to obtain, retain or direct business or obtain any improper advantage, in violation of the federal Foreign Corrupt Practices Act of 1977. Neither the sale of the Shares nor the use of proceeds from the sale thereof will result in a violation of the Trading with the Enemy Act, as amended, and any of the foreign assets control regulations of the United States Treasury Department (31 C.F.R., Subtitle B, Chapter V, as amended), or any ruling issued thereunder or any enabling legislation or Presidential Executive Order in connection therewith.

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4.22 Environmental and Safety Matters. Except as set forth on Schedule 4.22:

(a) The Company and its Subsidiaries have obtained all Environmental Permits and the validity of such Environmental Permits will not be affected by the consummation of this transaction.

(b) The Company and its Subsidiaries are in material compliance with the terms and conditions of all such Environmental Permits and is in material compliance with all Environmental and Safety Laws.

(c) With respect to the Company or any Subsidiary, no notice, notification, demand, request for information, citation, summons or order has been issued, no complaint has been served and no proceeding has been instituted and no penalty has been assessed or, to the Company’s knowledge, no investigation, notice, notification, demand, complaint, request for information, citation, summons, proceeding or order is pending or threatened by any Person with respect to any alleged failure to obtain any material Environmental Permits or any material violation of any Environmental Permits or Environmental and Safety Laws;

(d) No Hazardous Materials have been Released, placed, deposited, discharged, emitted or otherwise come to be located on, at or migrating from or to, any Real Property or, to the knowledge of the Company, at any previously owned, leased or operated property (during the period owned or used by the Company) or at any other property that will result in any material claim, liability or obligation of the Company or its Subsidiaries for cleanup of Hazardous Materials, bodily injury, property damage or natural resource damage, whether based upon or due to negligence or strict liability.

(e) No Real Property or any other property or facility now or previously owned, leased or operated by the Company or any Subsidiary has been (during the period owned or used by the Company) or is presently operated in a manner which requires permitting as a hazardous waste treatment, storage or disposal facility for purposes of RCRA or any analogous state law.

(f) To the Company’s knowledge, none of the following is present at any Real Property of the Company or any Subsidiary (except to the extent such presence could not reasonably be expected to result in a material liability): (i) polychlorinated biphenyls or radioactive materials contained in electrical, medical or other equipment; (ii) asbestos containing insulation or building material; or (iii) active or inactive aboveground or underground storage tanks.

(g) Neither the Company nor any Subsidiary has transported or arranged for the transportation of any Hazardous Material to any location which is on the CERCLA National Priorities List (or proposed for such listing), the CERCLIS List or any similar state list or which is the subject of federal, state or local enforcement Actions or other investigations which could reasonably be expected to lead to material claims against the Company or any Subsidiary under any Environmental and Safety Laws.

(h) No Liens have been imposed under or pursuant to any Environmental and Safety Laws on any Real Property now or any property previously owned, leased or operated by the Company or any Subsidiary, and to the knowledge of the Company, no governmental Actions have been taken or are in process which could subject any such properties or facilities to such Liens and the Company and its

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Subsidiaries has not been required to place any notice, restriction or engineering control relating to the presence of Hazardous Materials in any deed to such property or facility which would materially affect the business of the Company and its Subsidiaries as currently conducted.

(i) Neither the Company nor any Subsidiary has, either expressly or by operation of law, assumed or undertaken any material liability or corrective or remedial obligation of any other Person relating to Environmental and Safety Laws.

(j) Without limiting the generality of the foregoing, there are no other facts, events or conditions relating to the past (during the period owned or used by the Company) or present operations, properties or facilities of the Company or its Subsidiaries which could reasonably be expected to give rise to any material liability or investigatory, corrective or remedial obligation under any Environmental and Safety Laws.

4.23 Affiliated Transactions. Except as set forth on Schedule 4.23, no officer, director or Affiliate of the Company or any Subsidiary, or any individual directly related by blood, marriage or adoption to any such individual, or any entity in which any such Person or individual owns any beneficial interest, (i) is a party to any material agreement, contract, commitment or transaction with the Company or any Subsidiary or has any material interest in any material property used by the Company or any Subsidiary or (ii) owns, holds or possesses, directly or indirectly, any material financial or other interest in, or is a partner, member, manager, officer, director, employee or other Affiliate of (A) any Person that is a material supplier, vendor, customer, lessor, lessee, or competitor of the Company, any of its Subsidiaries or their businesses, or (B) any other business which engages in any material transactions or other business relationships with the Company or any of its Subsidiaries.

4.24 Investment Company. The Company is not an “investment company” as defined under the Investment Company Act of 1940.

4.25 Projections. The projections set forth on Schedule 4.25 were prepared in good faith. The Company does not, however, make any guaranty that any such projections can or will be achieved.

4.26 SEC Filings. None of the Company’s (1) annual report on Form 10 K, as amended, for the fiscal year ended December 31, 2005 and (2) quarterly reports on Form 10Q for the fiscal quarters ended March 31, 2006, June 30, 2006 and September 30, 2006 (the “Company’s SEC Documents”) contained, at the time they were filed, any untrue statement of a material fact or omitted to state any material fact required to be stated therein or necessary to make the statements made therein in light of the circumstances under which they were made, not misleading. The Company has timely filed all forms, reports and exhibits thereto required to be filed under the Securities Act and the Securities Exchange Act with the Securities and Exchange Commission.

4.27 Securities Laws. The Company has not offered to sell any portion of the Shares or any interest therein in a manner which violates any applicable securities law or would require the issuance and sale hereunder to be registered under the Securities Act.

4.28 Disclosure. Neither this Agreement nor any of the exhibits, schedules or certificates supplied by or on behalf of the Company at the Closing with respect to the

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transactions contemplated hereby, when taken together with the Company’s SEC Documents, contain any untrue statement of a material fact or omit a material fact necessary to make each statement contained herein or therein, under the circumstances in which they are made, not misleading. There is no fact which the Company has not disclosed to the Purchaser or in the Company’s SEC Documents and of which the Company has knowledge and which has had or would reasonably be expected to have a Material Adverse Effect.

Section 5. Representations and Warranties of the Purchaser. The Purchaser hereby represents and warrants to the Company as follows:

5.1 Authority of Purchaser. The Purchaser (a) is duly organized, validly existing and in good standing under the laws of the jurisdiction of its formation; (b) has all requisite legal and corporate or partnership power (as applicable) to enter into this Agreement and the Ancillary Agreements, to purchase the Shares and to perform its obligations under the terms of this Agreement and the Ancillary Agreements; and (c) has taken all corporate action (as applicable) necessary for the purchase of the Shares and the performance of the Purchaser’s obligations under this Agreement. The execution, delivery and performance by the Purchaser of this Agreement and the Ancillary Agreements has been duly authorized by the Purchaser. This Agreement and the Ancillary Agreements when executed and delivered by the Purchaser will constitute valid and legally binding obligations of the Purchaser, enforceable in accordance with their terms, except as enforcement may be limited by applicable bankruptcy laws or other similar laws affecting creditors’ rights generally, and except insofar as the availability of equitable remedies may be limited by applicable law from time to time.

5.2 Investment Representations.

(a) The Shares purchased hereunder and the shares of Common Stock issuable upon conversion of the Preferred Shares (the “Securities”) will be acquired for the Purchaser’s own account, not as a nominee or agent, and not with a view to the distribution of any part thereof in violation of securities laws.

(b) The Purchaser understands that the Securities have not been registered under the Securities Act or under similar securities laws of any other jurisdiction by reason of reliance upon certain exemptions therefrom, and that the reliance of the Company on such exemptions is predicated upon, among other things, the bona fide nature of the Purchaser’s investment intent as expressed herein. The Purchaser understands that the Securities being purchased hereunder are restricted securities within the meaning of Rule 144 under the Securities Act and that the Securities are not registered and must be held indefinitely unless they are subsequently registered or an exemption from such registration is available.

(c) The Purchaser is knowledgeable in business and financial matters and is capable of evaluating the merits and risks of an investment in the Company. The Purchaser acknowledges that it has the ability to bear the economic risk of its investment pursuant to this Agreement. The Purchaser is an “accredited investor” as defined in Rule 501(a) under the Securities Act.

(d) The Purchaser has not been organized or materially reorganized for the purpose of investing in the Securities.

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(e) The Purchaser represents, warrants and agrees that the sale of the Shares to it was not accomplished by the publication of any advertisement or by any general solicitation.

5.3 No Breach. The execution and delivery by the Purchaser of this Agreement and the Ancillary Agreements and the fulfillment of and compliance with the respective terms hereof and thereof by the Purchaser, do not and will not (i) conflict with or result in a breach of the terms, conditions or provisions of, (ii) constitute a default under, (iii) result in the creation of any Lien upon the Purchaser’s assets pursuant to, (iv) give any third party the right to modify, terminate or accelerate any obligation under, (v) result in a violation of, or (vi) require any authorization, consent, approval, exemption or other action by or notice or declaration to, or filing with, any Governmental Authority pursuant to, the charter or bylaws of the Purchaser, or any law, statute, rule or regulation to which the Purchaser is subject, or any agreement, instrument, order, judgment or decree to which the Purchaser is subject, except, (A) for any such authorization, consent, approval, exemption, action, notice, declaration or filing that has been previously obtained and (B) in the case of any of any agreement or instrument to which the Purchaser is subject, for such authorizations, consents or approvals that, if not so obtained, would not reasonably be expected to, individually or in the aggregate, result in a material adverse effect on the business, operations, prospects, financial condition, operating results or assets of the Purchaser or its Subsidiaries taken as a whole.

Section 6. Miscellaneous.

6.1 Governing Law. This Agreement shall be governed in all respects by, and any claim arising out of or relating to this Agreement, the transactions contemplated hereby or the negotiations or performance thereof shall be enforced pursuant to, the laws of the State of New York without application of principles of conflicts of law.

6.2 Submission to Jurisdiction. Each of the parties hereto hereby (a) agrees that any action, lawsuit or proceeding with respect to this Agreement may be brought only in the Supreme Court of the State of New York, County of New York, or of the United States District Court for the Southern District of New York, (b) accepts for itself and in respect of its property, generally and unconditionally, the exclusive jurisdiction of such courts for any such action lawsuit or proceeding, (c) irrevocably waives any objection, including, without limitation, any objection to the laying of venue or based on the grounds of forum non conveniens, which it may now or hereafter have to the bringing of any action, lawsuit or proceeding in those jurisdictions, and (d) irrevocably consents to the service of process of any of the courts referred to above in any such action, lawsuit or proceeding by the mailing of copies of the process to the parties hereto as provided in Section 6.6. Service effected as provided in this manner will become effective ten (10) calendar days after the mailing of the process. The parties hereto also may serve process in any such action, lawsuit or proceeding in any manner authorized by applicable law.

6.3 Survival; Limitation on Liability.

(a) The representations and warranties of the parties contained in this Agreement or in any certificate delivered pursuant hereto shall survive the Closing until June 21, 2008, and will survive thereafter with respect to any inaccuracy therein or breach thereof, written notice of which has been given to the Company by the Purchaser prior to such date; provided, however, that the representations and warranties set forth in

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Sections 4.1, 4.2, 4.3, 4.4, 4.12 and 4.22 will survive the Closing until June 21, 2010, and will survive thereafter with respect to any inaccuracy therein or breach thereof, written notice of which has been given to the Company by the Purchaser prior to such date.

(b) After the Closing, (i) no Person shall have liability for any claim or claims arising out of or relating to this Agreement (other than any claim or claims arising as a result of any inaccuracy or breach of the representations and warranties set forth in Sections 4.1, 4.2, 4.3 or 4.4), the transactions contemplated hereby, or the negotiation or performance thereof, in excess of $37,500,000 in the cumulative aggregate, regardless of the theory or theories of liability or Losses sought and (ii) no Person shall have liability for any claim or claims arising as a result of any inaccuracy or breach of the representations and warranties set forth in Sections 4.1, 4.2, 4.3 or 4.4 of this Agreement in excess of $150,000,000 in the cumulative aggregate, regardless of the theory or theories of liability or Losses sought.

(c) The parties agree that any claim or claims they may make or bring against the other party shall solely be for Losses incurred by such party due to, arising from or in connection with this Agreement, the transactions contemplated hereby or the negotiation or performance thereof. Notwithstanding any provision contained in Section 6.3 to the contrary, in the event any Loss incurred by the Purchaser is due to, arises from, or is in connection with, fraud by the Company or any Person acting or purporting to act on the Company’s behalf, the Purchaser will be entitled to recover any such Losses from the Company without regard to any of the limitations set forth above.

(d) All amounts due and owing from the Company with respect to any Losses covered under Section 6.3 shall be payable in cash.

6.4 Successors and Assigns; No Third Party Beneficiaries. The Purchaser may assign its interest in this Agreement in connection with any permitted transfer of its Shares. Except as otherwise expressly provided herein, the provisions hereof shall inure to the benefit of, and be binding upon, the successors, assigns, heirs, executors and administrators of the parties hereto. Nothing express or implied herein is intended or shall confer any right or remedy upon any Person not a party hereto.

6.5 Entire Agreement; No Reliance; Amendment. This Agreement and the Ancillary Agreements to be delivered pursuant hereto constitute the full and entire understanding and agreement between the parties with regard to the subjects hereof and thereof, and supercedes all prior and contemporaneous agreements, understandings or statements with respect thereto. No party is relying upon any representations, warranty, statement, agreement or understanding not expressly set forth in this Agreement or the Ancillary Agreements. Any term of this Agreement may be amended and the observance of any term of this Agreement may be waived (either generally or in a particular instance and either retroactively or prospectively), only with the written consent of the Company and the Purchaser.

6.6 Notices. All notices, requests, demands and other communications required to or permitted to be given under this Agreement shall be in writing and shall be conclusively deemed to have been duly given when hand delivered to the other party; when received when sent by facsimile; provided, however, that notices given by facsimile shall not be effective unless either a duplicate copy of such facsimile notice is promptly given by depositing same in a United States post office with first-class postage prepaid, or the receiving party

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delivers a written confirmation of receipt for such notice either by facsimile or any other method permitted under this paragraph; additionally, any notice given by facsimile shall be deemed received on the next business day if such notice is received after 5:00 p.m. (recipient’s time) or on a nonbusiness day; three (3) business days after the same has been deposited in a United States post office with first class or certified mail return receipt requested postage prepaid; or the next business day after same has been deposited with a national overnight delivery service, postage and fees prepaid with next business day delivery guaranteed; provided that the sending party receives a confirmation of delivery from the delivery service provider.

If notice is to be given to the Purchaser, such notice will be given, delivered or sent to:

Morgan Stanley Strategic Investments, Inc.

1585 Broadway – 2nd Floor

New York, New York 10036

Telephone number: (212) 761-1735 and (212) 761-1622

Facsimile number: (212) 507-2702 and (212) 507-4257

Attention: James E. Bolin and Thomas E. Doster.

If notice is to be given to the Company, such notice will be given, delivered or sent to:

US Oncology Holdings, Inc.

16825 Northchase Drive

Houston, TX 77060

Telephone number: (832) 601-6178

Facsimile number: (832) 601-6678

Attention: B. Scott Aitken

Each party shall make an ordinary, good faith effort to ensure that it will accept or receive notices that are given in accordance with this Section and that any person to be given notice actually receives such notice. A party may change or supplement its address for notice, or designate additional addresses, for purposes of this Section by giving the other party written notice of the new address in the manner set forth above.

6.7 Expenses. Each party shall bear its own expenses incurred in connection with the negotiation and execution of this Agreement and each Ancillary Agreement and the transactions contemplated hereby and thereby, except that at the Closing, the Company will reimburse the Purchaser for its reasonable and actual legal fees incurred by Richards Kibbe & Orbe LLP and accountant fees incurred by PriceWaterhouseCoopers LLP up to a maximum of One Hundred and Fifty Thousand Dollars ($150,000) in the aggregate. The Company has paid and shall remain solely responsible for all fees and expenses in connection with filings pursuant to the HSR Act.

If any action at law or in equity is necessary to enforce or interpret the terms of this Agreement, the prevailing party shall be entitled to reasonable attorneys’ fees, costs and necessary disbursements, at trial and on appeal, in addition to any other relief to which each party may be entitled.

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6.8 Delays or Omissions. No delay or omission to exercise any right, power or remedy accruing to any party, upon any breach or default of another party under this Agreement, shall impair any such right, power or remedy of such non breaching party, nor shall it be construed to be a waiver of any such breach or default, or an acquiescence therein, of any similar breach or default thereafter occurring; nor shall any waiver of any single breach or default be deemed a waiver of any other breach or default theretofore or thereafter occurring. Any waiver, permit, consent or approval of any kind or character on the part of any party under this Agreement, or any waiver on the part of any party of any provisions or conditions of this Agreement, must be in writing and shall be effective only to the extent specifically set forth in such writing. All remedies either under this Agreement, or by law or otherwise afforded to any party, shall be cumulative and not alternative.

6.9 Severability of this Agreement. In case any provision of this Agreement shall be held by a court of competent jurisdiction to be invalid, illegal or unenforceable, the validity, legality and enforceability of the remaining provisions shall not in any way be affected or impaired thereby.

6.10 Titles and Subtitles. The titles of the sections and subsections of this Agreement are for convenience of reference only and are not to be considered in construing this Agreement.

6.11 Counterparts. This Agreement may be executed in any number of counterparts, each of which shall be an original, but all of which together shall constitute one instrument.

6.12 Gender. The use of the neuter gender herein shall be deemed to include the masculine and feminine gender, if the context so requires.

6.13 Public Announcement. The Company shall not disclose the Purchaser’s name or identity as an investor in the Company in any press release or other public announcement or in any document or material filed with any Governmental Authority, without the prior consent of the Purchaser, unless such disclosure is required by applicable law or governmental or self-regulatory organization regulations or requirements or by order of a court of competent jurisdiction, in which case prior to making such disclosure the Company shall give written notice to the Purchaser describing in reasonable detail the proposed content of such disclosure and shall permit the Purchaser to review and comment upon the form and substance of such disclosure. Notwithstanding the foregoing, the Purchaser hereby acknowledge that, after the date hereof, the Company may attach this Agreement and any of the Ancillary Agreements as an exhibit or exhibits to reports filed by the Company with the Securities and Exchange Commission and may disclose the name of Purchaser and amount of shares held in such filings as required by applicable law or regulation.

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IN WITNESS WHEREOF, the parties have executed this Agreement as of the day and year set forth in the heading hereof.

THE COMPANY:

US ONCOLOGY HOLDINGS, INC.

By:

Name:

Title:

THE PURCHASER:

MORGAN STANLEY STRATEGIC INVESTMENTS, INC.

By:

Name:

Title:

EXHIBIT A

SECOND AMENDED AND RESTATED CERTIFICATE OF INCORPORATION OF US

ONCOLOGY HOLDINGS, INC.

EXHIBIT B

FORM OF AMENDED AND RESTATED STOCKHOLDERS AGREEMENT

EXHIBIT C

FORM OF AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT

EXHIBIT D

FORM OF OPINION OF COMPANY’S COUNSEL

EX-10.2

Exhibit 10.2

EXECUTION COPY

AMENDED AND RESTATED

STOCKHOLDERS AGREEMENT

AMENDED AND RESTATED STOCKHOLDERS AGREEMENT, dated as of December 21, 2006, by and among US ONCOLOGY HOLDINGS, INC. (formerly known as Oiler Holding Company), a Delaware corporation (the “Company”), WELSH, CARSON, ANDERSON & STOWE IX, L.P., a Delaware limited partnership (“WCAS IX”), MORGAN STANLEY STRATEGIC INVESTMENTS, INC., a Delaware corporation (“Morgan Stanley”), and each of the other individuals and entities from time to time named on Schedule I hereto (together with WCAS IX and Morgan Stanley, and together with their respective Permitted Transferees and their respective successors and assigns that become a party to this Agreement in accordance with the terms hereof, each a “Stockholder” and collectively, the “Stockholders”).

RECITALS

WHEREAS, the Company, WCAS IX and certain other Stockholders entered into the original Stockholders Agreement, dated as of August 20, 2004 (the “Original Stockholders Agreement”), to provide for certain matters relating to the shares of Participating Preferred Stock, par value $0.001 per share, of the Company (the “Series A Preferred Stock”), and the shares of Common Stock, par value $0.001 per share, of the Company (“Company Common Stock”), in each case, held by such Stockholders;

WHEREAS, the Company and Morgan Stanley have entered into a Stock Purchase Agreement, dated as of December 21, 2006 (the “Stock Purchase Agreement”), pursuant to which the Company has agreed to sell to Morgan Stanley shares of Series A-1 Participating Preferred Stock, par value $0.001 per share, of the Company (the “Series A-1 Preferred Stock” and together with the Series A Preferred Stock, the “Company Preferred Stock”) and shares of Company Common Stock; and

WHEREAS, in connection with the investment contemplated by the Stock Purchase Agreement, the Company, WCAS IX and certain other Stockholders wish to amend and restate the Original Stockholders Agreement in the manner set forth herein;

NOW, THEREFORE, in consideration of the premises and of the mutual covenants and agreements herein contained, the parties hereto hereby agree as follows:

ARTICLE I.

INTRODUCTORY MATTERS

SECTION 1.01. Defined Terms. In addition to the terms defined elsewhere herein, the following terms have the following meanings when used herein with initial capital letters:

“Affiliate” means, with respect to any specified Person, a Person that directly, or indirectly through one or more intermediaries, Controls, is Controlled by or is under common Control with, the specified Person; provided, that officers, directors or employees of the Company or USON will not be deemed to be Affiliates of a stockholder of the Company for purposes hereof solely by reason of being officers, directors or employees of the Company or USON; provided, further, that, for purposes of Section 8.02(vi) and the definition of Third Party contained in Section 4.01, no portfolio company of WCAS IX (or of any other investment partnership under common control with WCAS IX) shall be deemed to be an Affiliate of the Company or WCAS IX unless a majority of the outstanding voting securities or 25% or more of the economic interests of such portfolio company are owned, directly or indirectly, by WCAS IX and/or such other investment partnership.

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“Agreement” means this Agreement, as the same may be amended, supplemented or otherwise modified from time to time in accordance with the terms hereof.

“Assumption Agreement” means a writing reasonably satisfactory in form and substance to the Company and WCAS IX whereby a Permitted Transferee of Company Equity Securities becomes a party to, and agrees to be bound (to the same extent as its transferor) by, the terms of this Agreement as a “Stockholder” hereunder.

“Board” means the Board of Directors of the Company.

“Business Day” means a day other than a day on which commercial banks in New York, New York or Houston, Texas are authorized or required by law to close.

“Commission” means the Securities and Exchange Commission, or any other federal agency at the time administering the Securities Act.

“Company Capital Stock” means the Company Common Stock, the Company Preferred Stock and any other class or series of capital stock or other equity stock of the Company.

“Company Certificate” means the Second Amended and Restated Certificate of Incorporation of the Company, as amended, restated or modified.

“Company Equity Securities” means all shares of Company Capital Stock now or hereafter issued and all Options or Convertible Securities now or hereafter issued.

“Company Stock Plans” means all stock option plans, restricted stock purchase plans and other stock-based employee benefit plans and agreements approved by the Board, including the Company’s 2004 Equity Incentive Plan.

“Control” (including the terms “Controlling”, “Controlled by” and “under common Control with”) means the possession, direct or indirect, of the power to direct or cause the direction of the management and policies of a Person, whether through the ownership of voting securities, by contract or otherwise.

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“Designated Affiliate” means (i) in the case of any Stockholder that is not a natural person, any Affiliate of such Stockholder, (ii) in the case of a Stockholder who is a natural person, such Stockholder’s parents, spouse and lineal descendants and the lineal descendants of such Stockholder’s spouse, or trusts for the benefit of, or corporations, limited liability companies or partnerships, the stockholders, members or general and/or limited partners of which include, only such Stockholder and/or Stockholder’s parents, spouse or lineal descendants or the lineal descendants of such Stockholder’s spouse, (iii) in the case of WCAS IX and each of its Designated Affiliates under this clause (iii), WCAS IX and each general or limited partner, manager, member, officer, director or employee thereof, and (iv) in the case of Morgan Stanley and each of its Designated Affiliates under this clause (iv), Morgan Stanley and each stockholder, partner, manager, member, director or officer thereof. For purposes of the foregoing, lineal descendants shall be deemed to include children by adoption.

“Exchange Act” means the Securities Exchange Act of 1934, or any successor federal statute, and the rules and regulations of the Commission thereunder, as the same may be amended from time to time.

“Fully Diluted Basis” means, with respect to any determination of the number of shares of Company Common Stock outstanding or held by one or more Persons, the number of shares of Company Common Stock outstanding or held by such Persons (excluding any unvested shares of restricted Company Common Stock issued under Company Stock Plans) assuming (i) the conversion of each outstanding share of Company Preferred Stock into that number of shares of Company Common Stock equal to the Conversion Constant (as defined in Section I of Article FOURTH of the Company Certificate) as in effect at the time of such determination and (ii) the full conversion, exercise and exchange of all other Options or Convertible Securities for Company Common Stock (excluding options and other rights issued under Company Stock Plans and excluding any other Options or Convertible Securities which are not exercisable or which have not vested or shares received upon the exercise of such Options or Convertible Securities which would not be vested); provided, however, that in connection with a Proposed Sale (as defined in Section 3.01(a)), unvested shares of restricted Company Common Stock issued under Company Stock Plans which would vest at or before the consummation of such Proposed Sale shall not be excluded from the determination of the number of shares of Company Common Stock held by a Tagging Stockholder; provided, further, however, that in connection with determining whether a Stockholder is a Qualified Stockholder or determining a Qualified Stockholder’s Proportionate Percentage for purposes of Article V, unvested shares of restricted Company Common Stock issued under Company Stock Plans shall not be excluded from the determination of the number of shares of Company Common Stock held by such Stockholder.

“Options or Convertible Securities” means any securities (including, without limitation, any options, warrants or other rights) which are directly or indirectly convertible into or exercisable or exchangeable for Company Capital Stock.

“Permitted Transferee” means any (i) Person to whom Company Equity Securities are Transferred in a Transfer in accordance with Section 2.02 and otherwise not in violation of this Agreement and who enters into an Assumption Agreement and (ii) Person to whom Company Equity Securities are Transferred by any Stockholder in a Transfer in accordance with Section 2.01(a)(i) who agrees in writing to become a party to and agrees to be bound (to the

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same extent as its transferor) by, the terms of this Agreement as a “Stockholder” hereunder, it being understood, in each case, that neither the Company nor any of its Subsidiaries shall be considered to be Permitted Transferees.

“Person” means any natural person, corporation, limited liability company, partnership, trust, joint stock company, business trust, unincorporated association, joint venture, governmental authority or other legal entity of any nature whatsoever.

“Public Offering” means the sale of shares of Company Common Stock to the public pursuant to an effective registration statement (other than a registration statement on Form S-4, Form S-8 or any similar or successor form) filed under the Securities Act.

“Qualified Merger” means the consummation of any sale of all then outstanding Company Equity Securities (whether by means of a merger or otherwise), or sale of all or substantially all of the Company’s assets to, a Third Party, if the holders of shares of Company Equity Securities, as consideration for such sale, directly or indirectly, receive equity securities which are tradable on a national securities exchange (i) without further registration under the Securities Act and (ii) without being subject to any volume limitations set forth in Rule 144 promulgated under the Securities Act.

“Qualified Public Offering” means any firm commitment underwritten Public Offering in which the aggregate proceeds to the Company (together with the aggregate proceeds in all such prior public offerings) are at least $100.0 million.

“Qualified Stockholder” means any Stockholder who (individually or together with its Designated Affiliates), at the time of determination, holds on a Fully Diluted Basis not less than 500,000 shares (as adjusted for any stock splits, stock dividends, stock combinations and similar events occurring after the date hereof) of Company Common Stock.

“Schedule IV Purchaser” means any Schedule IV Purchaser under and as defined in the Stock Subscription Agreement (which Stockholders are listed on Schedule I hereto under the heading “Schedule IV Purchasers”) so long as such Stockholder continues to own, collectively with its Permitted Transferees, at least 50% of the shares of Company Common Stock and 50% of the shares of Company Preferred Stock owned by it on August 20, 2004 after giving effect to the transactions contemplated by the Stock Subscription Agreement.

“Securities Act” means the Securities Act of 1933, or any successor federal statute, and the rules and regulations of the Commission thereunder, as the same may be amended from time to time.

“Stock Subscription Agreement” means the Stock Subscription and Exchange Agreement, dated as of August 20, 2004, by and among the Company, WCAS IX and certain Stockholders.

“Subsidiary” of a Person means any Person of which equity securities or other ownership interests having ordinary voting power to elect a majority of the board of directors, the general partner, the manager or other Persons performing similar functions are at the time

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directly or indirectly owned by the Person. Unless the context otherwise requires, references to one or more Subsidiaries are references to Subsidiaries of the Company.

“Transfer” means a transfer, sale, assignment, pledge, hypothecation or other disposition (including by operation of law), whether directly or indirectly pursuant to the creation of a derivative security, the grant of an option or other right or the imposition of a restriction on disposition or voting.

“USON” means US Oncology, Inc., a Delaware corporation, and a wholly owned Subsidiary of the Company.

“Voting Proxy” means any irrevocable proxy granted to WCAS IX by a Stockholder and shall include each “Voting Proxy” referred to in the Stock Subscription Agreement.

SECTION 1.02. Construction. (a) The parties hereto have participated jointly in the negotiation and drafting of this Agreement. In the event an ambiguity or question of intent or interpretation arises, this Agreement shall be construed as if drafted jointly by the parties and no presumption or burden of proof shall arise favoring or disfavoring any party by virtue of the authorship of any provisions of this Agreement. Unless the context otherwise requires: (i) “or” is disjunctive but not exclusive, (ii) words in the singular include the plural, and in the plural include the singular, (iii) the words “hereof”, “herein”, and “hereunder” and words of similar import when used in this Agreement refer to this Agreement as a whole and not to any particular provision of this Agreement, (iv) the headings contained in this Agreement are for reference purposes only and shall not affect in any way the meaning or interpretation of this Agreement, (v) the words “Article” and “Section” are references to the articles and sections of this Agreement unless otherwise specified and (vi) whenever the words “include”, “includes” or “including” are used in this Agreement they shall be deemed to be followed by the words “without limitation”.

(b) References herein to WCAS IX, to the extent such entity shall have transferred any of its shares of Company Capital Stock to one or more Permitted Transferees, shall mean WCAS IX and such Permitted Transferees, taken together, and any right or action that may be taken at the election of WCAS IX may be taken at the election of WCAS IX and such Permitted Transferees to the extent WCAS IX has agreed in writing to transfer such rights to any such Permitted Transferee.

(c) References herein to Morgan Stanley, to the extent such entity shall have transferred any of its shares of Company Capital Stock to one or more Permitted Transferees, shall mean Morgan Stanley and such Permitted Transferees, taken together, and any right or action that may be taken at the election of Morgan Stanley may be taken at the election of Morgan Stanley and such Permitted Transferees to the extent Morgan Stanley has agreed in writing to transfer such rights to any such Permitted Transferee.

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ARTICLE II.

TRANSFERS

SECTION 2.01. Transfers. (a) No Stockholder may Transfer any Company Equity Securities other than:

(i) with respect to Transfers by Stockholders other than by WCAS IX, Transfers made with the written consent of WCAS IX; provided, that, notwithstanding the foregoing, any employee, officer or director of the Company or any of its subsidiaries may Transfer Company Equity Securities to the Company or any of its Subsidiaries; provided, further, that notwithstanding the foregoing, in the case of any proposed Transfer by Morgan Stanley or any of its Permitted Transferees after the third anniversary of the date hereof, such written consent of WCAS IX will not be unreasonably withheld, delayed or conditioned;

(ii) Transfers made in accordance with Section 2.02;

(iii) Transfers made in accordance with Article III (including any Excluded Transactions (as defined in Section 3.01(a)); or

(iv) Transfers made in accordance with Article IV.

Any attempted Transfer of Company Equity Securities in violation of the provisions of this Agreement shall be null and void ab initio and of no effect.

(b) Each certificate representing Company Equity Securities that is held by a Stockholder will bear a legend substantially to the following effect with such additions thereto or changes therein as the Company may be advised by counsel are required by law or necessary to give full effect to this Agreement (the “Stockholders Agreement Legend”):

“THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO A STOCKHOLDERS AGREEMENT, AMENDED AND RESTATED AS OF DECEMBER 21, 2006, AMONG THE COMPANY AND THE OTHER PARTIES THERETO, AS AMENDED, A COPY OF WHICH IS ON FILE WITH THE SECRETARY OF THE COMPANY. NO TRANSFER, SALE, ASSIGNMENT, PLEDGE, HYPOTHECATION OR OTHER DISPOSITION OF THE SECURITIES REPRESENTED BY THIS CERTIFICATE MAY BE MADE EXCEPT IN ACCORDANCE WITH THE PROVISIONS OF SUCH STOCKHOLDERS AGREEMENT. THE HOLDER OF THIS CERTIFICATE, BY ACCEPTANCE OF THIS CERTIFICATE, AGREES TO BE BOUND BY ALL OF THE PROVISIONS OF SUCH STOCKHOLDERS AGREEMENT.”

The Stockholders Agreement Legend will be removed by the Company by the delivery of substitute certificates without such Stockholders Agreement Legend in the event of (i) a Transfer permitted by this Agreement in which the Transferee is not required to enter into an Assumption Agreement or (ii) the termination of this Agreement in accordance with Section 10.07.

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(c) The Company shall not give effect to any attempted Transfer of Company Equity Securities made in violation of the terms of any Voting Proxy, and any attempted Transfer in violation of the terms thereof shall be null and void ab initio and of no effect. At all times prior to the expiration of any Voting Proxy, the Company shall use its best efforts to comply with the provisions of such Voting Proxies relating to the placing of legends on Company Equity Securities, and each Stockholder granting any such Voting Proxy hereby consents to the placing of such legends on such certificates.

SECTION 2.02. Transfers to Permitted Transferees. Any Stockholder may, at any time, Transfer any or all of the Company Equity Securities held by such Stockholder to any one or more Designated Affiliates of such Stockholder so long as each such Designated Affiliate duly executes and delivers an Assumption Agreement (such Transfer to be effective only upon the delivery of such Assumption Agreement to the Company and WCAS IX); provided, that if the Company so requests promptly following (and, in any event, within five (5) Business Days after) its receipt of such Assumption Agreement, such Assumption Agreement shall not be effective unless and until the Company has been furnished with an opinion in form and substance reasonably satisfactory to the Company of counsel reasonably satisfactory to the Company that such Transfer is exempt from or not subject to the provisions of Section 5 of the Securities Act and any other applicable securities laws. Notwithstanding the foregoing, no party hereto shall avoid the provisions of this Agreement by making one or more Transfers to one or more Permitted Transferees and then disposing of all or any portion of such party’s interest in any such Permitted Transferee.

SECTION 2.03. Securities Law Compliance. (a) Each Stockholder agrees that it will not effect any Transfer of Company Equity Securities held by such Stockholder unless such Transfer is made pursuant to an effective registration statement under the Securities Act or pursuant to an exemption from, or in a transaction not subject to, the registration requirements of the Securities Act and, in either case, in compliance with all applicable state securities laws. The Company agrees, and each Stockholder understands and consents, that (i) the Company will not cause or permit the Transfer of any Company Equity Securities to be made on its books (or on any register of securities maintained on its behalf) unless the Transfer is permitted by, and has been made in accordance with the terms of this Agreement and all applicable federal and state securities laws and (ii) no Transfer of Company Equity Securities under this Article II shall be permitted if such Transfer would require the Company to register a class of equity securities under Section 12 of the Exchange Act under circumstances where the Company does not then have securities of any class registered under Section 12 of the Exchange Act. Any attempted Transfer in violation of the terms hereof shall be null and void ab initio and of no effect. Each Stockholder agrees that in connection with any Transfer of Company Equity Securities that is not made pursuant to a registered public offering, the Company may, in its sole discretion, request an opinion in form and substance reasonably satisfactory to the Company of counsel reasonably satisfactory to the Company stating that such transaction is exempt from registration under the Securities Act and in compliance with applicable state securities laws.

(b) From and after the date hereof, and until such time as such securities have been sold to the public pursuant to an effective registration statement under the Securities Act or pursuant to an exemption from such registration and the holder of such securities shall have requested the issuance of new certificates in writing and, if requested by the Company, delivered

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to the Company an opinion in form and substance reasonably satisfactory to the Company of counsel reasonably satisfactory to the Company to such effect, all certificates representing Company Equity Securities that are held by any Stockholder shall bear a legend which shall state the following:

“THE SECURITIES EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND NO INTEREST HEREIN MAY BE SOLD, OFFERED, ASSIGNED, DISTRIBUTED, PLEDGED OR OTHERWISE TRANSFERRED UNLESS (A) THERE IS AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT COVERING ANY SUCH TRANSACTION OR (B) THE COMPANY RECEIVES AN OPINION IN FORM AND SUBSTANCE REASONABLY SATISFACTORY TO THE COMPANY OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY STATING THAT SUCH TRANSACTION IS EXEMPT FROM SUCH REGISTRATION AND IN COMPLIANCE WITH ALL APPLICABLE STATE SECURITIES LAWS OR (C) THE COMPANY AND ITS COUNSEL ARE OTHERWISE SATISFIED THAT SUCH TRANSACTION IS EXEMPT FROM SUCH REGISTRATION AND IN COMPLIANCE WITH ALL STATE SECURITIES LAWS.”

ARTICLE III.

TAG-ALONG RIGHTS

SECTION 3.01. Tag-Along Rights. (a) With respect to any proposed Transfer by WCAS IX and/or any of its Permitted Transferees (collectively, the “Selling Stockholder”) of shares of Company Capital Stock to any Person who is not a Designated Affiliate of the Selling Stockholder other than (i) pursuant to any agreement or plan of merger or combination, including any tender or exchange offer in respect thereof, that is approved by the Board and does not involve a disproportionate Transfer by the Selling Stockholder of shares of the applicable class of Company Capital Stock or (ii) any transaction or transactions for strategic purposes that (when aggregated with all shares sold in connection with prior Transfers that were deemed to be Excluded Transactions under this clause (ii)) result in the Transfer by the Selling Stockholder since August 20, 2004 of (x) less than an aggregate 1,069,106 (as adjusted for any stock splits, stock dividends, stock combinations and similar events occurring after August 20, 2004) shares of Company Preferred Stock and/or (y) less than an aggregate 7,483,744 shares (as adjusted for any stock splits, stock dividends, stock combinations and similar events occurring after August 20, 2004) of Company Common Stock (any such transaction referred to in clause (i) or (ii) above, an “Excluded Transaction”, and any such transaction not excluded under clause (i) or (ii) above, a “Proposed Sale”), each Stockholder (other than the Selling Stockholder) who exercises its rights under this Section 3.01(a) in accordance with this Section 3.01 (each a “Tagging Stockholder”) will have the right to include the following in the proposed sale to the proposed transferee(s) of shares (the “Proposed Transferee”) or sell the following to the Selling Stockholder (if such Proposed Transferee will not agree to purchase shares directly from such Tagging Stockholder, and in such case the Selling Stockholder shall be obligated to purchase from such Stockholder the following): (1) if the Selling Stockholder proposes to Transfer shares of Company Preferred Stock in such Proposed Sale, a number of shares of Company Preferred Stock up to the product (rounded down to the nearest whole number) of (i) the quotient

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determined by dividing (A) the aggregate number of shares of Company Preferred Stock owned by such Tagging Stockholder by (B) the aggregate number of shares of Company Preferred Stock then outstanding and (ii) the total number of shares of Company Preferred Stock proposed to be Transferred to the Proposed Transferee(s) and/or (2) if the Selling Stockholder proposes to Transfer shares of Company Common Stock in such Proposed Sale, a number of shares of Company Common Stock up to the product (rounded down to the nearest whole number) of (i) the quotient determined by dividing (A) the aggregate number of shares of Company Common Stock owned by such Tagging Stockholder on a Fully Diluted Basis by (B) the aggregate number of shares of Company Common Stock then outstanding on a Fully Diluted Basis and (ii) the total number of shares of Company Common Stock proposed to be Transferred to the Proposed Transferee(s), at the same price(s) per share of Company Preferred Stock and/or Company Capital Stock, as the case may be, and upon the same terms and conditions (including time of payment, form of consideration and adjustments to purchase price) as the Selling Stockholder; provided, that in order to be entitled to exercise its right to sell shares of Company Capital Stock to the Proposed Transferee pursuant to this Section 3.01, each Tagging Stockholder (x) shall agree to the same covenants as the Selling Stockholder agrees to in connection with the Proposed Sale, (y) shall be obligated to join on a pro rata (and several) basis (based on the proceeds received by such Tagging Stockholder in connection with the Proposed Sale) in any indemnification that the Selling Stockholder agrees to provide in connection with the Proposed Sale (other than in connection with obligations that relate to a particular Stockholder such as representations and warranties concerning itself for which each Stockholder shall agree to be solely responsible, and provided further that the liability for any such pro rata (and several) indemnification obligations shall not exceed the total consideration received by such Stockholder for such shares), and (z) shall make such representations and warranties concerning itself and the shares of Company Capital Stock to be sold by it in connection with such Transfer as the Selling Stockholder makes with respect to itself and its shares (such terms and conditions of any Proposed Sale being the “Tag-Along Terms”).

(b) Each Tagging Stockholder will be responsible for funding its proportionate share of any adjustment in purchase price or escrow arrangements in connection with the Proposed Sale and for its proportionate share of any withdrawals from any such escrow, including any such withdrawals that are made with respect to claims arising out of agreements, covenants, representations, warranties or other provisions relating to the Proposed Sale.

(c) Each Tagging Stockholder will be responsible for its proportionate share of the fees, commissions and other out-of-pocket expenses (collectively, “Costs”) of the Proposed Sale to the extent not paid or reimbursed by the Company, the Proposed Transferee or another Person (other than the Selling Stockholder); provided, that the liability for such Costs shall not exceed the total purchase price received by such Stockholder for such shares (or if such Proposed Sale does not occur, such proposed purchase price). The Selling Stockholder shall be entitled to estimate each Tagging Stockholder’s proportionate share of such Costs and to withhold such amounts from payments to be made to each Tagging Stockholder at the time of closing of such Proposed Sale; provided, that (i) such estimate shall not preclude the Selling Stockholder from recovering additional amounts from the Tagging Stockholders in respect of each such Tagging Stockholder’s proportionate share of such Costs and (ii) the Selling Stockholder shall reimburse each Tagging Stockholder to the extent actual amounts are

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ultimately less than the estimated amounts or any such amounts are paid by the Company, the Proposed Transferee or another Person (other than the Selling Stockholder).

SECTION 3.02. Exercise of Tag-Along Rights; Notices. The Selling Stockholder will give the Company prior written notice of each Proposed Sale, setting forth the number and type of shares of Company Capital Stock proposed to be so Transferred, the name and address of the Proposed Transferee, the proposed amount and form of consideration and other material Tag-Along Terms offered by the Proposed Transferee. In the event that any of the material terms or conditions set forth in the notice are thereafter amended in any material respect, the Selling Stockholder shall also give written notice of the amended terms and conditions of the Proposed Sale to the Company. Upon its receipt of any such notice or amended notice, the Company shall promptly, but in all events within two (2) Business Days of its receipt thereof, forward copies thereof to each of the Stockholders other than the Selling Stockholder (such initial notice, the “Tag-Along Opportunity Notice” and any amended notice, an “Amended Tag-Along Opportunity Notice”). In order to exercise the tag-along rights provided by this Article III a Stockholder must send a written notice to the Company and the Selling Stockholder indicating its desire to exercise its rights and specifying the number and type of shares of Company Capital Stock it desires to sell (the “Tag-Along Exercise Notice”) within ten (10) days following the receipt of the Tag-Along Opportunity Notice by such Stockholder (or if an Amended Tag-Along Opportunity Notice is given to the Stockholders within such ten (10) day period, within five (5) days following the receipt of such Amended Tag-Along Opportunity Notice by such Stockholder). Upon the receipt of an Amended Tag-Along Opportunity Notice by a Stockholder that had previously provided a Tag-Along Exercise Notice, such Tagging Stockholder shall be permitted to cancel its exercise of its rights under this Article III upon delivery of written notice to the Selling Stockholder and the Company to such effect and shall be released from its obligation hereunder. There shall be no liability on the part of the Selling Stockholder to any Tagging Stockholder if the sale of shares of Company Capital Stock pursuant to this Article III is not consummated for whatever reason. Whether or not to effect a sale of shares of Company Capital Stock pursuant to this Article III shall be within in the sole and absolute discretion of the Selling Stockholder.

SECTION 3.03. Closing of Proposed Sale. (a) Each Tagging Stockholder shall deliver to the Company, as agent for such Tagging Stockholder, for transfer to the Proposed Transferee one or more certificates, properly endorsed for transfer and with all stock transfer taxes paid and stamps affixed, which represent the shares of Company Capital Stock that such Tagging Stockholder is permitted to dispose of pursuant to this Article III. The consummation of such Proposed Sale shall be subject to the sole discretion of the Selling Stockholder, who shall have no liability or obligation whatsoever to any Tagging Stockholder participating therein other than to obtain for such Tagging Stockholder the same Tag-Along Terms as those of the Selling Stockholder. In connection with the consummation of any such Proposed Sale, the Company (i) shall transfer to the Proposed Transferee at the closing of such Proposed Sale a stock certificate or certificates representing the shares of Company Capital Stock to be disposed of by any Tagging Stockholders and (ii) shall promptly thereafter remit to each Tagging Stockholder (x) that portion of the proceeds of the disposition to which such Tagging Stockholder is entitled by reason of such participation (after giving effect to Section 3.01(b) and/or 3.01(c)) and (y) a stock certificate or certificates representing any balance of shares of Company Capital Stock that were not so disposed of (or all shares of Company Capital Stock, in the event the proposed disposition

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is not consummated). For the avoidance of doubt, the Selling Stockholder may not Transfer any shares of Company Capital Stock to the Proposed Transferee unless the Proposed Transferee shall simultaneously purchase, in accordance with Tag-Along Terms, all of shares of Company Capital Stock to be disposed of by any Tagging Stockholders in accordance with this Article III.

(b) If any Tagging Stockholder exercises its rights under this Article III, the closing of the purchase of the Company Capital Stock with respect to which such rights have been exercised will take place concurrently with the closing of the sale of the Selling Stockholder’s Company Capital Stock to the Proposed Transferee. If by the end of ninety (90) days following the date of delivery of the Tag-Along Opportunity Notice (or, following the delivery of the last Amended Tag-Along Opportunity Notice, if applicable), the Selling Stockholder and the Proposed Transferee have not completed the Proposed Sale, each Tagging Stockholder shall be released from its obligations under this Article III, and the Tag-Along Exercise Notices shall be null and void, and it shall be necessary for the terms of this Article III to be separately complied with in order to consummate such Proposed Sale pursuant to this Article III.

SECTION 3.04. Tag-Along Power of Attorney. Upon delivering a Tag Along Exercise Notice, each Tagging Stockholder will, if requested by the Selling Stockholder, execute and deliver a power of attorney in form and substance reasonably satisfactory to the Selling Stockholder with respect to the shares of Company Capital Stock that are to be sold by such Tagging Stockholder pursuant hereto (a “Tag-Along Power of Attorney”). The Tag-Along Power of Attorney will provide, among other things, that each such Tagging Stockholder will irrevocably appoint said attorney-in-fact as its agent and attorney-in-fact with full power and authority to act under the Tag-Along Power of Attorney on its behalf with respect to (and subject to the terms and conditions of) the matters specified in this Article III.

ARTICLE IV.

DRAG-ALONG RIGHTS

SECTION 4.01. Drag-Along Rights. If WCAS IX (the “Dragging Stockholder”), the Company or USON receives an offer from a Person who is not an Affiliate of the Company or WCAS IX (a “Third Party”) to purchase or exchange (by merger, consolidation or otherwise) (x) at least a majority of the shares of Company Common Stock then outstanding and/or at least a majority of the shares of Company Preferred Stock then outstanding or (y) all or substantially all of the assets of the Company and its subsidiaries taken as a whole, and WCAS IX wishes to accept such offer (or WCAS IX wishes that the Company or USON accept such offer), then each Stockholder other than WCAS IX (the “Drag-Along Stockholders”) hereby agrees that, if requested by the Dragging Stockholder, such Stockholder will (A) waive any appraisal rights that it would otherwise have in respect of such transaction, and/or (B) Transfer to such Third Party, subject to the other provisions of this Article IV, on the terms of the offer so accepted by the Dragging Stockholder, including time of payment, form and choice of consideration and adjustments to purchase price, (i) the number of shares of Company Preferred Stock equal to the number of shares of Company Preferred Stock owned by such Stockholder multiplied by the percentage of the then outstanding shares of Company Preferred Stock to which the Third Party offer is applicable, if any, and (ii) the number of shares of Company Common Stock equal to the

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number of outstanding shares of Company Common Stock owned by such Stockholder multiplied by the percentage of the then outstanding shares of Company Common Stock to which the Third Party offer is applicable, if any.

SECTION 4.02. Exercise of Drag-Along Rights; Notices; Certain Conditions of Drag-Along Sales. (a) The Dragging Stockholder will give notice (the “Drag-Along Notice”) to the Drag-Along Stockholders of any proposed Transfer giving rise to the rights of the Dragging Stockholder set forth in Section 4.01 (a “Drag-Along Sale”) within five (5) Business Days after the Dragging Stockholder’s acceptance of the offer referred to in Section 4.01 and, in any event, not less than fifteen (15) Business Days prior to the proposed closing date for such Drag-Along Sale. The Drag-Along Notice will set forth the number and type of shares of Company Capital Stock proposed to be so Transferred, the name of the proposed transferee or acquiring Person, the proposed amount and form of consideration, the number and type of shares of Company Capital Stock sought and the other terms and conditions of the offer.

(b) If any holders of Company Capital Stock are given an option as to the form and amount of consideration to be received, all holders of such class of Company Capital Stock shall be given the same option. Each Drag-Along Stockholder (x) shall agree to the same covenants as the Dragging Stockholder agrees to in connection with the Drag-Along Sale, (y) shall be obligated to join on a pro rata (and several) basis (based on the proceeds received by each such Drag-Along Stockholder in connection with the Drag-Along Sale) in any indemnification that the Dragging Stockholder agrees to provide in connection with the Drag-Along Sale (other than in connection with obligations that relate to a particular Stockholder such as representations and warranties concerning itself for which each Stockholder shall agree to be solely responsible, and provided further that the liability for any such pro rata indemnification obligations shall not exceed the total consideration received by such Stockholder for such shares) and (z) shall make such representations and warranties concerning itself and the shares of Company Capital Stock to be sold by it in connection with such Drag-Along Sale as the Dragging Stockholder makes with respect to itself and its shares.

(c) Each Drag-Along Stockholder will be responsible for funding its proportionate share of any adjustment in purchase price or escrow arrangements in connection with the Drag-Along Sale and for its proportionate share of any withdrawals from any such escrow, including any such withdrawals that are made with respect to claims arising out of agreements, covenants, representations, warranties or other provisions relating to the Drag-Along Sale.

(d) Each Drag-Along Stockholder will be responsible for its proportionate share of the Costs of the Drag-Along Sale to the extent not paid or reimbursed by the Company, the Third Party or another Person (other than the Dragging Stockholder); provided, that the liability for such Costs shall not exceed the total consideration received by such Drag-Along Stockholder for its Company Equity Securities in respect of such Drag-Along Sale. The Dragging Stockholder shall be entitled to estimate each Drag-Along Stockholder’s proportionate share of such Costs and to withhold such amounts from payments to be made to each Drag-Along Stockholder at the time of closing of the Drag-Along Sale; provided that (i) such estimate shall not preclude the Dragging Stockholder from recovering additional amounts from the Drag-Along Stockholders in respect of each Drag-Along Stockholder’s proportionate share of such

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Costs and (ii) the Dragging Stockholder shall reimburse each Drag-Along Stockholder to the extent actual amounts are ultimately less than the estimated amounts or any such amounts are paid by the Company, the Third Party or another Person (other than the Dragging Stockholder).

SECTION 4.03. Closing of Drag-Along Sale. (a) At the closing of such Drag-Along Sale, each of the Drag-Along Stockholders shall deliver certificates evidencing the Company Equity Securities then held by it and to be sold or cancelled in connection with such sale, duly endorsed for transfer or accompanied by stock powers executed in blank, against payment of the purchase price therefor by wire transfer to the account or accounts specified by such Drag-Along Stockholder.

(b) If the Drag-Along Sale is not consummated within 120 days from the date of the Drag-Along Notice, the Dragging Stockholder must deliver another Drag-Along Notice in order to exercise its rights under this Article IV with respect to such Drag-Along Sale.

SECTION 4.04. Custody Agreement and Power of Attorney. Upon receiving a Drag-Along Notice, each Drag-Along Stockholder will, if requested by the Dragging Stockholder, execute and deliver a custody agreement and power of attorney in form and substance reasonably satisfactory to the Dragging Stockholder with respect to the shares of Company Capital Stock that are to be sold by such Drag-Along Stockholder pursuant hereto and with respect to any other Company Equity Securities subject to this Article IV in respect of such Drag-Along Sale (a “Drag-Along Custody Agreement and Power of Attorney”). The Drag-Along Custody Agreement and Power of Attorney will provide, among other things, that each such Drag-Along Stockholder will deliver to and deposit in custody with the custodian and attorney-in-fact named therein a certificate or certificates representing such shares of Company Capital Stock (each duly endorsed in blank by the registered owner or owners thereof) and irrevocably appoint said custodian and attorney-in-fact as its agent and attorney-in-fact with full power and authority to act under the Drag-Along Custody Agreement and Power of Attorney on its behalf with respect to (and subject to the terms and conditions of) the matters specified in this Article IV.

ARTICLE V.

PREEMPTIVE RIGHTS

SECTION 5.01. Grant of Preemptive Rights. The Company hereby grants to each Qualified Stockholder the right to purchase such Qualified Stockholder’s Proportionate Percentage (as hereinafter defined) of any Company Equity Securities to be issued in any future Eligible Issuance (as hereinafter defined). For the purposes of this Article V, the following terms shall have the meanings set forth below:

“Proportionate Percentage” means, with respect to any Qualified Stockholder as of any date, the result (expressed as a percentage) obtained by dividing (i) the number of shares of Company Common Stock owned by such Qualified Stockholder as of such date on a Fully Diluted Basis by (ii) the total number of shares of Company Common Stock outstanding as of such date on a Fully Diluted Basis.

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“Eligible Issuance” means the issuance by the Company to any Person or Persons (including any of the Stockholders) for cash, cash equivalents, property or indebtedness of any Company Equity Securities, other than an issuance by the Company:

(i) of shares of Company Common Stock or options to purchase shares of Company Common Stock in connection with or pursuant to (x) a Company Stock Plan or (y) any offering to physicians affiliated with the Company;

(ii) of Company Equity Securities in connection with a bona fide business acquisition, reorganization or recapitalization of or by the Company or any Subsidiary thereof, whether by merger, consolidation, sale of assets, sale or exchange or otherwise;

(iii) of Company Equity Securities to any Person with which the Company has business relationships provided that such issuances are for other than primarily equity financing purposes;

(iv) of Company Equity Securities upon the exercise, exchange or conversion of Options or Convertible Securities;

(v) of Company Equity Securities to a lender (including any Stockholder or any of their Designated Affiliates) in connection with a debt financing or the amendment of any debt financing arrangements; or

(vi) of Company Equity Securities in a Public Offering.

SECTION 5.02. Notice of Eligible Issuance. The Company shall, before issuing any Company Equity Securities in an Eligible Issuance, give written notice thereof to each Qualified Stockholder. Such notice shall specify the Company Equity Securities the Company proposes to issue, the proposed date of issuance, the consideration that the Company intends to receive therefor and all other material terms and conditions of such proposed issuance. For a period of ten (10) days following the date of receipt of such notice, each Qualified Stockholder shall be entitled, by written notice to the Company, to elect to purchase all or any part of such Qualified Stockholder’s Proportionate Percentage of the Company Equity Securities being sold in the Eligible Issuance; provided, that if two or more securities shall be proposed to be sold as a “unit” in an Eligible Issuance, any such election must relate to such unit of securities. To the extent that elections pursuant to this Section 5.02 shall not be made with respect to any Company Equity Securities included in an Eligible Issuance within such ten (10) day period, then the Company may issue such Company Equity Securities, but only for consideration not less than, and otherwise on terms no less favorable to the Company than, those set forth in the Company’s notice and only within ninety (90) days after the end of such ten (10) day period. In the event that any such offer is accepted by one or more Qualified Stockholder or Qualified Stockholders, the Company shall sell to such Qualified Stockholder or Qualified Stockholders, and such Qualified Stockholder or Qualified Stockholders shall purchase from the Company, for the consideration and on the terms set forth in the notice as aforesaid, the securities that such Qualified Stockholder or Qualified Stockholders shall have elected to purchase and the Company

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may sell the balance, if any, of the Company Equity Securities it proposed to sell in such Eligible Issuance in accordance with the immediately preceding sentence. Notwithstanding anything to the contrary contained above, if the Board shall have determined that it is in the best interests of the Company to proceed with an Eligible Issuance prior to providing the notices required by this Article V or affording each of the Qualified Stockholders its preemptive rights in strict compliance with this Article V, the Company shall be permitted to first consummate such issuance (the buyer of such shares in such issuance is referred to herein as the “Buyer”) and thereafter deliver such notices and afford the Qualified Stockholders an opportunity to exercise their preemptive rights hereunder so long as such notices are delivered and such preemptive rights offer is conducted as soon as practicable thereafter and such offer is structured such that (i) each Qualified Stockholder shall have the right to buy at the same price and on the same terms as the Buyer and (ii) after giving effect to the exercise of its preemptive rights in connection with such Eligible Issuance in full, such Qualified Stockholder shall hold the same Proportionate Percentage of Company Equity Securities that it held immediate prior to such Eligible Issuance.

ARTICLE VI.

INFORMATION RIGHTS

SECTION 6.01. Information Rights. Unless the Company has timely filed periodic reports with the Securities and Exchange Commission pursuant to the Exchange Act or any indenture or other agreement governing indebtedness of the Company, the Company shall provide to Morgan Stanley (so long as it is a Qualified Stockholder), each of its Permitted Transferees (so long as such Permitted Transferee is a Qualified Stockholder) and each Schedule IV Purchaser, by electronic means or otherwise, (a) annual audited financial statements within 90 days of the end of the Company’s fiscal year, and (b) a statement of operations within 45 days of the end of each of the Company’s first three fiscal quarters, each prepared in accordance with generally accepted accounting principles. Without limiting the foregoing, from and after the date hereof, on reasonable prior written notice, the Company shall make its directors, officers, key employees, lawyers, accountants, agents and other consultants of the Company reasonably available to such Stockholders to discuss the business, results of operations and other matters pertaining to the Company, it being understood and agreed that no Schedule IV Purchaser shall be permitted to exercise the rights granted pursuant to this sentence more than two (2) times in any fiscal year. In addition, (i) the Company shall provide Morgan Stanley (so long as it is a Qualified Stockholder) and each of its Permitted Transferees (so long as such Permitted Transferee is a Qualified Stockholder) copies of all information delivered to the Company’s stockholders or senior lenders and such other financial information that is distributed to the members of the Board; and (ii) Morgan Stanley (so long as it is a Qualified Stockholder), each of its Permitted Transferees (so long as such Permitted Transferee is a Qualified Stockholder) and their respective representatives will have the right, upon reasonable prior written notice to the Company and only at times during normal business hours and which would not cause undue disruption to the Company’s business or operations, to visit and inspect the Company’s properties and examine the corporate and financial records of the Company; provided, such Stockholder may not exercise the right set forth in clause (ii) more than two (2) times in any fiscal year. Any and all information provided to any such Stockholder pursuant to the terms of this Article VI shall be subject to the agreements with respect to Confidential Information (as hereinafter defined) set forth in Article VII.

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ARTICLE VII.

CONFIDENTIALITY

SECTION 7.01. Confidential Information. (a) Each Stockholder agrees that it will not use at any time any Confidential Information of which any such Stockholder is or becomes aware except in connection with determining the interest of the Stockholder in entering into a transaction with the Company.

(b) Each Stockholder further agrees that the Confidential Information will be kept strictly confidential and will not be disclosed by it or its Representatives (as defined below), except (i) as required by applicable law, rule regulation or legal process or in response to any inquiry from a regulatory authority having jurisdiction over such Stockholder, and only after compliance with Section 7.01(c) and (ii) that it may disclose the Confidential Information or portions thereof to those of its officers, employees, members, managers, directors, advisors, financing sources, bona fide potential transferees and other agents and representatives (the persons to whom such disclosure is permissible being “Representatives”) who need to know such information in connection with the investment by the Stockholder in the Company; provided that such Representatives (x) are informed of the confidential and proprietary nature of the Confidential Information and (y) agree to maintain such confidentiality in accordance with the provisions of this Article VII. Each Stockholder agrees to be responsible for any breach of this Article VII by its Representatives (it being understood that such responsibility shall be in addition to and not by way of limitation of any right or remedy the Company may have against such Representatives with respect to any such breach).

(c) If any Stockholder or Representative thereof becomes legally compelled (including by deposition, interrogatory, request for documents, subpoena, civil investigative demand, regulatory agency or stock exchange rule or similar process) to disclose any of the Confidential Information, such Stockholder or Representative shall provide the Company with prompt and, if legally permissible, prior written notice of such requirement to disclose such Confidential Information. Upon receipt of such notice, the Company may seek a protective order or other appropriate remedy. If such protective order or other remedy is not obtained, such Stockholder and its Representatives shall disclose only that portion of the Confidential Information which is legally required to be disclosed and shall take all reasonable steps to preserve the confidentiality of the Confidential Information. In addition, neither such Stockholder nor its Representative will oppose any action (and such Stockholder and its Representatives will, if and to the extent requested by the Company and legally permissible to do so, cooperate with and assist the Company, at the Company’s expense and on a reasonable basis, in any reasonable action) by the Company to obtain an appropriate protective order or other reliable assurance that confidential treatment will be accorded the Confidential Information.

(d) As used herein, “Confidential Information” means oral and written information concerning the Company and its subsidiaries furnished to any Stockholder or Representative thereof by or on behalf of the Company (irrespective of the form of communication and whether such information is so furnished before, on or after the date hereof), and all analyses, compilations, data, studies, notes, interpretations, memoranda or other documents prepared by any Stockholder or any Representative thereof containing or based in

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whole or in part on any such furnished information. The term “Confidential Information” does not, with respect to any Stockholder, include any information which (i) at the time of disclosure or thereafter is generally available to the public (other than as a result of a disclosure directly or indirectly by such Stockholder or its Representative in violation hereof), (ii) is or becomes available to such Stockholder or its Representatives on a non-confidential basis from a source other than the Company or its advisors provided that such source was not known by such Stockholder or its Representatives to be prohibited from disclosing such information to such Stockholder by a legal, contractual or fiduciary obligation, (iii) with respect to any Stockholder that is an investment partnership or government pension plan, the identity of the Company or the amount invested in Company Capital Stock by such Stockholder, (iv) was already in the possession of Stockholder or its Representatives prior to receiving such information from the Company or its advisors, or (v) was developed independently by Stockholder or its Representatives without use of the Confidential Information.

(e) The provisions of this Article VII shall terminate and be of no further force or effect on the earlier to occur of (i) the termination of this Agreement as set forth in Section 10.07 herein or and (ii) the date which is one year from the date such Stockholder no longer holds any Company Equity Securities.

ARTICLE VIII.

VOTING AGREEMENT

SECTION 8.01. Election of Directors. (a) Each Stockholder hereby agrees to cast all votes to which such Stockholder is entitled in respect of his, her or its shares of Company Capital Stock, whether at any annual or special meeting, by written consent or otherwise, to:

(i) fix the number of members of the Board at a number specified from time to time by WCAS IX, which number shall be at least two;

(ii) for so long as Morgan Stanley or any of its Permitted Transferees shall hold any shares of Company Capital Stock, elect as members of the Board one (1) individual designated by Morgan Stanley or its Permitted Transferees and reasonably acceptable to WCAS IX (such approval not to be unreasonably withheld, delayed or conditioned);

(iii) elect as members of the Board such number of individuals designated by WCAS IX equal to the authorized number of directors less the one director designated pursuant to clause (ii) above; and

(iv) remove from the Board (with or without cause) any director elected in accordance with this Section 8.01 upon the written request of the Stockholder that designated and continues to have the right to designate such director (it being understood that no Stockholder shall vote for or consent to and the Company shall not take any actions to effect any other removal (with or without cause) of a director elected pursuant to this Section 8.01 without the written consent of the Stockholder that designated and continues to have the right to designate such director).

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(b) If, as a result of death, disability, retirement, resignation or removal (with or without cause), there shall exist or occur any vacancy of the Board:

(i) the Person entitled to designate or nominate such director whose death, disability, retirement or removal resulted in such vacancy may designate another individual (the “Nominee”) to fill such capacity and serve as a director of the Company; and

(ii) each Stockholder then entitled to vote for the election of the Nominee as a director of the Company agrees that it will vote its shares of Company Capital Stock in order to ensure that the Nominee be elected to the Board.

(c) Each Stockholder will vote such Stockholder’s shares of Company Capital Stock or execute written consents, as the case may be, and the Company and each Stockholder will take all other actions as may be reasonably necessary or appropriate (including, if applicable, calling or causing the Company to call a special meeting of its stockholders), to carry out the purposes and intent of this Section 8.01.

SECTION 8.02. Special Protective Provisions. At any time when shares of Series A-1 Preferred Stock are outstanding, in addition to any other vote required by law, without the prior written consent of the holders of not less than a majority of the outstanding shares of Series A-1 Preferred Stock held by Morgan Stanley and its Permitted Transferees (which consent will not be unreasonably withheld, delayed or conditioned), the Company will not and will not permit any Subsidiary to:

(i) increase the total number of shares of Series A-1 Preferred Stock authorized to be issued by the Company Certificate;

(ii) create, obligate itself to create, authorize or issue any new class or series of Company Equity Securities having preference over the Series A-1 Preferred Stock with respect to payment of dividends, redemption payments or payment upon liquidation, dissolution or winding-up of the Company;

(iii) enter into any transaction that would result in a Change of Control (as defined in the Company Certificate), other than (A) any such transaction that is permitted in accordance with Articles III, IV or V of this Agreement or (B) any such transaction pursuant to which the holders of Company Preferred Stock receive the same consideration per share (other than differences that may result from differences in the Accreted Value (as defined in the Company Certificate) of such shares) and all holders of Company Common Stock receive the same consideration per share;

(iv) authorize, declare or set aside or pay any dividend or other distribution to holders of Company Capital Stock, other than (A) the one-time

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distribution to holders of Series A Preferred Stock and Common Stock on or about the date hereof and contemplated by the Stock Purchase Agreement, (B) Regular Dividends (as defined in the Company Certificate) which are paid to all holders of Company Preferred Stock in accordance with paragraph 2 of the Company Certificate, (C) distributions made in accordance with paragraphs 3, 4 or 5 of the Company Certificate, or (D) dividends or other distributions which are made to all holders of Company Preferred Stock on a pro rata basis (subject to differences that may result from differences in the Accreted Value of such shares);

(v) authorize or make any repurchase or redemption of any shares of Company Equity Securities, other than (A) repurchases or redemptions in accordance with paragraphs 3 or 5 of the Company Certificate, (B) repurchases or redemptions in accordance with agreements with employees of the Company or any Subsidiary that are approved by the Board or (C) other repurchases or redemptions in which all holders of Company Preferred Stock have the right to participate on a pro rata basis (subject to differences that may result from differences in the Accreted Value of such shares);

(vi) enter into any material transaction with any Affiliate of the Company, other than (A) any such transaction permitted in accordance with Article V of this Agreement, (B) any such transaction that is permitted by the provisions of the Indenture, dated March 29, 2005, between the Company and LaSalle Bank National Association, as Trustee, relating to the Company’s outstanding senior floating rate notes due 2015 or (C) any such transaction with Morgan Stanley or any Affiliate of Morgan Stanley that is approved by the Board (for avoidance of doubt, any Excluded Transaction or Proposed Sale permitted in accordance with Article III and any Drag-Along Sale to a Third Party permitted in accordance with Article IV shall not be considered a material transaction with an Affiliate of the Company for purposes of this Section 8.02(vi)); and

(vii) consummate any Public Offering that is not a Qualified Public Offering or cause USON to consummate the sale of shares of common stock of USON to the public pursuant to an effective registration statement (other than a registration statement on Form S-4, Form S-8 or any similar or successor form).

ARTICLE IX.

REPRESENTATIONS AND WARRANTIES

SECTION 9.01. Representations and Warranties by the Stockholders. Each Stockholder, severally and not jointly, represents and warrants to the Company and the other Stockholders as follows:

(a) The execution, delivery and performance of this Agreement by such Stockholder will not violate any provision of applicable law, any order of any court or other agency of government, the certificate or articles of incorporation, bylaws, operating agreement,

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partnership agreement or other organizational documents of such Stockholder or any provision of any indenture, agreement or other instrument to which such Stockholder or any of such Stockholder’s properties or assets is bound, or conflict with, result in a breach of or constitute (with due notice or lapse of time or both) a default under any such indenture, agreement or other instrument.

(b) This Agreement has been duly executed and delivered by such Stockholder, and, when executed by the other parties hereto, will constitute the legal, valid and binding obligation of such Stockholder, enforceable against such Stockholder in accordance with its terms.

SECTION 9.02. Representations and Warranties by the Company. The Company represents and warrants to each Stockholder as follows:

(a) The execution, delivery and performance of this Agreement by the Company will not violate any provision of applicable law, any order of any court or other agency of government, the Company Certificate or the Company’s Bylaws or any provision of any indenture, agreement or other instrument to which the Company or any of its properties or assets is bound, or conflict with, result in a breach of or constitute (with due notice or lapse of time or both) a default under any such indenture, agreement or other instrument.

(b) This Agreement has been duly executed and delivered by the Company, and, when executed by the other parties hereto, will constitute the legal, valid and binding obligation of the Company, enforceable against the Company in accordance with its terms.

ARTICLE X.

MISCELLANEOUS

SECTION 10.01. Severability. In the event that any one or more of the provisions contained in this Agreement or in any other instrument referred to herein shall, for any reason, be held to be invalid, illegal or unenforceable, such illegality, invalidity or unenforceability shall not affect any other provisions of this Agreement.

SECTION 10.02. Benefits of Agreement. Nothing expressed by or mentioned in this Agreement is intended or shall be construed to give any Person other than the parties hereto and their respective successors and permitted assigns any legal or equitable right, remedy or claim under or in respect of this Agreement or any provision herein contained, this Agreement and all conditions and provisions hereof being intended to be and being for the sole and exclusive benefit of the parties hereto and their respective successors and permitted assigns. Notwithstanding anything in this Section 10.02 to the contrary, subject to compliance with the terms of this Agreement, each Stockholder shall have the right to assign its rights hereunder in whole or in part to any transferee of the Company Equity Securities held by such Stockholder in compliance with this Agreement (including Section 2.02) . Except as expressly permitted hereby, each party’s rights and obligations under this Agreement shall not be subject to assignment or delegation by any party hereto, and any attempted assignment or delegation in violation hereof shall be null and void ab initio.

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SECTION 10.03. Notice of Transfer. To the extent that any Stockholder shall Transfer any Company Equity Securities, notice of which Transfer is not otherwise required to be delivered to the Stockholders hereunder, such Stockholder shall, within three (3) days following consummation of such Transfer, deliver notice thereof to the Company and WCAS IX.

SECTION 10.04. Notices. Any notice or communication required or permitted hereunder shall be in writing and shall be delivered personally, delivered by nationally recognized overnight courier service, sent by certified or registered mail, postage prepaid, or sent by facsimile (subject to confirmation by return facsimile of such facsimile transmission). Any such notice or communication shall be deemed to have been received (i) when delivered, if personally delivered, (ii) one (1) Business Day after it is deposited with a nationally recognized overnight courier service, if sent by nationally recognized overnight courier service, (iii) the day of sending, if sent by facsimile prior to 5:00 p.m. (EST) on any Business Day or the next succeeding Business Day if sent by facsimile after 5:00 p.m. (EST) on any Business Day or on any day other than a Business Day or (iv) five Business Days after the date of mailing, if mailed by certified or registered mail, postage prepaid, in each case, to the following address or facsimile number, or to such other address or addresses or facsimile number or numbers as such party may subsequently designate to the other parties by notice given hereunder:

if to the Company, to it at:

16825 Northchase Drive

Houston, Texas 77060

Facsimile: (832) 601-6688

Attention: Chief Executive Officer

with a copy to:

Welsh, Carson, Anderson & Stowe IX, L.P.

320 Park Avenue, Suite 2500

New York, New York 10022

Attention: D. Scott Mackesy

Facsimile: (212) 893-9566

with an additional copy to:

Ropes & Gray LLP

45 Rockefeller Plaza

New York, New York 10111

Attention: Othon A. Prounis, Esq.

Facsimile: (212) 841-5725

if to any Stockholder, to such Stockholder at the address set forth opposite such Stockholder’s name on Schedule I hereto.

SECTION 10.05. Entire Agreement; Modification. This Agreement constitutes the entire agreement among the parties with respect to the subject matter hereof and supersedes

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all prior agreements and understandings, both oral and written, among the parties with respect to the subject matter hereof. This Agreement may not be amended, modified or waived except by an instrument in writing signed by the Company, WCAS IX and Stockholders other than WCAS IX (the “Other Stockholders”) holding not less than a majority of the shares of Company Common Stock held by the Other Stockholders on a Fully Diluted Basis; provided, that, (i) no provision of this Agreement may be amended, modified or waived in a manner materially adverse to any Other Stockholder (in its capacity as a Stockholder hereunder) if such amendment, modification or waiver adversely affects such Other Stockholder disproportionately relative to the other Other Stockholders (disregarding for such purposes differences resulting solely from the amount of Company Equity Securities held by the Other Stockholders) except with the written consent of such adversely and disproportionately effected Other Stockholder, (ii) no provision of Article III may be amended, modified or waived in any manner that would diminish the rights of any Schedule IV Purchaser unless such Schedule IV Purchaser consents in writing to such amendments, modifications or waivers (such consent not to be unreasonably withheld or delayed) and (iii) no provision of this Agreement may be amended, modified or waived in any manner that would diminish the rights of Morgan Stanley or any of its Permitted Transferees unless the holders of a majority of the Company Equity Securities held by Morgan Stanley and its Permitted Transferees consents in writing to such amendments, modifications or waivers (such consent not to be unreasonably withheld or delayed); provided, further, that, notwithstanding the foregoing, in accordance with Article II or upon the written agreement of the Company and WCAS IX, additional Stockholders may be added to this Agreement (it being understood that any amendment of the provisions of this Agreement in connection with the addition of new Stockholders to this Agreement does not require the prior written consent of the Schedule IV Purchasers or Morgan Stanley and its Permitted Transferees, as the case may be, so long as (i) in the case of the Schedule IV Purchasers, no provision of Article III is amended in any manner that would diminish the rights of any Schedule IV Purchaser and (ii) in the case of the Morgan Stanley and its Permitted Transferees, no provision of this Agreement is amended in a manner adverse to any of Morgan Stanley or its Permitted Transferees). Except as otherwise provided herein, any waiver of any provision of this Agreement must be in a writing signed by the party against whom enforcement of such waiver is sought. Notwithstanding anything to the contrary in this Section 10.05, the Company and any Stockholder or Stockholders may agree among themselves to terms and conditions that are different from the terms and conditions set forth in this Agreement.

SECTION 10.06. Covenants Bind Successors and Assigns. All the covenants, stipulations, promises and agreements in this Agreement contained by or on behalf of any party shall bind its successors and permitted assigns, whether so expressed or not.

SECTION 10.07. Duration of Agreement. This Agreement (other than the provisions of Section 2.03 and Article VII which shall survive the termination of this Agreement) shall terminate upon the earliest to occur of (x) a Qualified Public Offering or (y) a Qualified Merger. This Agreement shall terminate with respect to any Stockholder when such Stockholder ceases to be a holder of any shares of Company Preferred Stock or Company Common Stock.

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SECTION 10.08. Counterparts. This Agreement may be executed in any number of counterparts, and each such counterpart hereof shall be deemed to be an original instrument, but all such counterparts together shall constitute but one agreement.

SECTION 10.09. Changes in Company Common Stock. If, and as often as, there are any changes in Company Common Stock by way of stock split, stock dividend, combination or reclassification, or through merger, consolidation, reorganization or recapitalization, or by any other means, appropriate adjustment shall be made in the provisions hereof as may be required so that the rights and privileges granted hereby shall continue with respect to the Company Common Stock as so changed.

SECTION 10.10. Specific Performance. Each party hereto agrees that a remedy at law for any breach or threatened breach by such party of this Agreement would be inadequate and therefore agrees that any other party hereto shall be entitled to pursue specific performance of this Agreement in addition to any other available rights and remedies in case of any such breach or threatened breach.

SECTION 10.11. Governing Law. This Agreement, and all claims arising hereunder or relating hereto, shall be governed and construed and enforced in accordance with the laws of the State of New York.

SECTION 10.12. Waiver Of Jury Trial. EACH OF THE PARTIES HERETO HEREBY IRREVOCABLY WAIVES ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING ARISING OUT OF OR RELATED TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY.

[SIGNATURE PAGES FOLLOW]

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IN WITNESS WHEREOF, each of the parties hereto has duly executed and delivered this Stockholders Agreement as of the date first written above.

THE COMPANY:

US ONCOLOGY HOLDINGS, INC.

By:

Name:

Title:

WCAS IX:

WELSH, CARSON, ANDERSON & STOWE IX, L.P.
By:	WCAS IX Associates LLC, its General Partner
By:
Name:
Title:

MORGAN STANLEY:

MORGAN STANLEY STRATEGIC
INVESTMENTS, INC.

By:

Name:

Title:

OTHER STOCKHOLDERS:

WCAS MANAGEMENT CORPORATION
By:
Name:
Title:
Russell L. Carson Bruce K. Anderson Thomas E. McInerney Robert A. Minicucci Anthony J. de Nicola Paul B. Queally D. Scott Mackesy D. Scott Mackesy – IRA Charles Schwab & Co., Inc. Custodian Sanjay Swani John D. Clark – IRA Charles Schwab & Co., Inc. Custodian John D. Clark James R. Matthews – IRA Charles Schwab & Co., Inc. Custodian Jonathan M. Rather – IRA Charles Schwab & Co., Inc. Custodian Sean M. Traynor John Almeida Rona Drogy Dave Mintz Clinton Biondo Ankar Kumar Michael E. Donovan Brian Regan Eric J. Lee
By:
Name:	Jonathan M. Rather
Title:	Attorney-in-Fact

THE PATRICK WELSH 2004
IRREVOCABLE TRUST

By:

Name:

Title:

R. Dale Ross

Lloyd K. Everson, M.D.

Phillip H. Watts

Bruce D. Broussard

George D. Morgan

Leo E. Sands

Atul Dhir, M.B.B.S., D. Phil

ROSS RESOURCES LIMITED

By:

Name:

Title:

Schedule I to Amended and Restated Stockholders Agreement

Stockholders

Address for Notices

Welsh, Carson, Anderson & Stowe IX, L.P. WCAS Management Corporation Russell L. Carson Bruce K. Anderson The Patrick Welsh 2004 Irrevocable Trust Thomas E. McInerney Robert A. Minicucci Anthony J. de Nicola Paul B. Queally D. Scott Mackesy Sanjay Swani John D. Clark IRA f/b/o John D. Clark IRA f/b/o D. Scott Mackesy IRA f/b/o James R. Matthews IRA f/b/o Jonathan M. Rather Sean M. Traynor John Almedia, Jr. Stacey Bellet* Suzanne Bellet Price* Rona Drogy David Mintz Clinton M. Biondo Ankur Kumar Michael E. Donovan Brian T. Regan Eric J. Lee Jill A. Hanau

c/o Welsh, Carson, Anderson & Stowe 320 Park Avenue, Suite 2500 New York, New York 10022 Attention: D. Scott Mackesy Facsimile: (212) 893-9566

* Additional copy to:

125 East 72nd Street

Apt. 11-D

New York, NY 10021

Attention: David F. Bellet

Robert A. Ortenzio Rocco A. Ortenzio c/o Select Capital Corporation 4718 Old Gettysburg Road, Suite 405 Mechanicsburg, PA 17055 Attention: Robert Nause Facsimile: (717) 972-1080

Stockholders	Address for Notices
Melkus Partners Melkus Family Foundation The Lauren Evelyn Melkus Trust Lauren Melkus	c/o Kenneth J. Melkus 102 Woodmont Blvd., Suite 110 Nashville, TN 37203 Facsimile: (615) 383-0104
Joelle M. Kayden	c/o Accolade Partners, L.P. 7900 Westpark Drive, Suite T-602 McLean, VA 22102 Facsimile: (703) 749-7800
Weigers & Co. LLC Betsy Weigers 2002 Unit Trust George A. Weigers 2001 Unit Trust	c/o Weigers Capital Management, LLC 55 Madison Street, Suite 680 Denver, CO 80206
Kyle M. Fink, M.D.	PBM 391 0105 Edwards Village Blvd., C104 Edwards, CO 81632
Texas Oncology, P.A.	c/o R. Steven Paulson, M.D. 12221 Merit Drive, Suite 500 Dallas, TX 75251
R. Dale Ross Lloyd K. Everson, M.D. Phillip H. Watts Bruce D. Broussard George D. Morgan Leo E. Sands Atul Dhir, M.B.B.S., D. Phil Ross Resources Limited Richard J. Hall	c/o US Oncology, Inc. 16825 Northchase Drive Houston, TX 77060 Attention: R. Dale Ross Facsimile: (832) 601-6688

Stockholders	Address for Notices
Schedule IV Purchasers:
California State Teachers’ Retirement System	7667 Folsom Boulevard, Suite 250 Sacramento, CA 95826 Attention: Real Desrochers and Seth Hall Facsimile: (916) 229 3790
Gunners Investment Pte Ltd.	c/o GIC Special Investments Pte Ltd. 255 Shoreline Drive, Suite 600 Redwood City, CA 94065 Attention: Andrew Kwee Facsimile: (650) 802-1213
Abu Dhabi Investment Authority	P.O. Box 3600 Corniche Street Abu Dhabi United Arab Emirates Attention: Abubaker Al Khouri Facsimile: (971 2) 626-4616
A.S.F. Co-Investment Partners II, L.P.	c/o IBM Retirement Funds 3001 Summer Street, MD 49 Stamford, CT 06905 Attention: Betty Sheets Facsimile: (203) 316-2190 With a copy to: c/o Portfolio Advisors, LLC 9 Old Kings Highway South Darien, CT 06820 Attention: Hugh Perloff Facsimile: (203) 662-0013

EX-10.3

Exhibit 10.3

EXECUTION COPY

AMENDED AND RESTATED

REGISTRATION RIGHTS AGREEMENT

AMENDED and RESTATED REGISTRATION RIGHTS AGREEMENT, dated as of December 21, 2006, among US ONCOLOGY HOLDINGS, INC., a Delaware corporation (the “Company”), WELSH, CARSON, ANDERSON & STOWE IX, L.P., a Delaware limited partnership (“WCAS”), MORGAN STANLEY STRATEGIC INVESTMENTS, INC., a Delaware corporation (“Morgan Stanley”), and each of the other individuals and entities from time to time named on Schedule I hereto (together with WCAS and Morgan Stanley, and together with their respective successors and assigns that become a party to this Agreement in accordance with the terms hereof, each an “Investor” and collectively, the “Investors”).

RECITALS

WHEREAS, the Company, WCAS and certain of the Investors entered into the original Registration Rights Agreement, dated as of August 20, 2004 (the “Original Registration Rights Agreement”) in connection with the acquisition by such Investors of shares of Participating Preferred Stock, par value $0.001 per share, of the Company (the “Series A Preferred Stock”), and the shares of Common Stock, par value $0.001 per share, of the Company (“Common Stock”);

WHEREAS, the Company and Morgan Stanley have entered into a Stock Purchase Agreement, dated as of December 21, 2006 (the “Stock Purchase Agreement”), pursuant to which the Company has agreed to sell to Morgan Stanley shares of Series A-1 Participating Preferred Stock, par value $0.001 per share, of the Company (the “Series A-1 Preferred Stock” and together with the Series A Preferred Stock, the “Participating Preferred Stock”) and shares of Common Stock; and

WHEREAS, in connection with the investment contemplated by the Stock Purchase Agreement, the Company, WCAS and certain other Investors wish to amend and restate the Original Registration Rights Agreement in the manner set forth herein;

NOW, THEREFORE, in consideration of the premises and the mutual covenants and agreements herein contained and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto, intending to be legally bound, hereby agree as follows:

SECTION 1. Certain Definitions. For purposes of this Agreement, the following terms have the meanings set forth below:

“Commission” means the Securities and Exchange Commission, or any other federal agency at the time administering the Securities Act.

“Exchange Act” means the Securities Exchange Act of 1934, or any successor federal statute, and the rules and regulations of the Commission thereunder, as the same may be amended from time to time.

“Initiating Investor” means, with respect to any Demand Registration, the Investor or Investors who initially deliver the Demand Request applicable to such Demand Registration.

“IPO Date” means the first date on which Common Stock shall have been sold by the Company in a Public Offering.

“Public Offering” means the sale of shares of Common Stock to the public pursuant to an effective registration statement (other than a registration statement on Form S-4 or S-8 or any successor form) filed under the Securities Act.

“Registrable Stock” means, at any time, (x) all shares of Common Stock now or hereafter held by the Investors, including all shares from time to time issued or issuable upon the conversion, exercise or exchange of any securities directly or indirectly convertible into or exercisable or exchangeable for Common Stock (other than (i) options issued pursuant to any stock option plan, including the Company’s 2004 Equity Incentive Plan, and (ii) shares of restricted stock (including shares of Common Stock issued pursuant to the Company’s 2004 Equity Incentive Plan) that will not have vested before the earliest anticipated effective date of the registration statement for any proposed offering of such restricted stock pursuant to this Agreement), that are now or hereafter held by the Investors, including the Participating Preferred Stock (it being understood that, with respect to any determination hereunder of the number of shares of Registrable Stock at any time held by one or more Investors, all such shares of Common Stock that are issuable upon any such conversion, exercise or exchange shall be deemed to have been issued at the time of such determination) and (y) any shares of Common Stock issuable with respect to the foregoing by way of stock dividend or stock split or in connection with a combination of shares, recapitalization, merger, consolidation or other reorganization or otherwise; provided, that, with respect to the Company’s initial Public Offering only, “Registrable Stock” shall mean, with respect to each Investor, only that number of shares of Common Stock issued or issuable upon the related conversion, if any, of the shares of Participating Preferred Stock then held by such Investor at the time of such conversion (assuming for such purposes that the Conversion Constant (such term being used herein as defined in the Company’s certificate of incorporation) at such time is zero (0). As to any particular Registrable Stock, such shares shall cease to be Registrable Stock (i) when a registration statement with respect to the sale of such shares shall have been declared effective under the Securities Act and such shares shall have been disposed of in accordance with such registration statement, (ii) when such shares shall have been sold (other than in a privately negotiated sale) pursuant to Rule 144 (or any successor provision) under the Securities Act, (iii) when, with respect to the holder thereof, such shares can be sold pursuant to Rule 144 promulgated under the Securities Act within a three month period without any volume limitation or (iv) when, with respect to the holder thereof, all such shares held by such holder become eligible for sale under Rule 144(k) of the Securities Act (or any similar or successor rule).

“Securities Act” means the Securities Act of 1933, or any successor federal statute, and the rules and regulations of the Commission thereunder, as the same may be amended from time to time.

SECTION 2. Registration Rights.

(a) Demand Registration Rights. Subject to Section 2(c) below, if the Company shall (i) at any time on or after the date hereof, be requested by WCAS or (ii) at any time on or after the date which is one hundred and eighty (180) days after the IPO Date, be requested by Morgan Stanley (provided, however, that a request by Morgan Stanley may be made under this Section 2(a) within such 180 day period and upon receipt of any such request, the Company shall take actions to prepare the Demand Registration for filing; provided, further, however, that the Company shall not be obligated to file with the SEC such Demand Registration until a date which is 180 days after the IPO Date), in each case, in a writing that states the number of shares of Registrable Stock to be sold and the intended method of disposition thereof (each such written request, a “Demand Request”), to effect a registration under the Securities Act of all or any portion of the Registrable Stock then held by the Investors, the Company shall immediately notify in writing (each such notice, a “Demand Registration Notice”) each other Investor of such proposed registration and shall use its commercially reasonable efforts to register under the Securities Act (each such registration, a “Demand Registration”), for public sale in accordance with the method of disposition specified in such Demand Request, the number of shares of Registrable Stock specified in such Demand Request (plus the number of shares of Registrable Stock specified in any written request for registration of shares of Registrable Stock that is received from each other Investor receiving the Demand Registration Notice within 20 days after receipt by such other Investor of such Demand Registration Notice). In addition, with the written consent of the Initiating Investor, the Company shall be entitled to include in any Demand Registration, for sale in accordance with the method of disposition specified by such Investor, shares of Common Stock to be sold by the Company for its own account or for the account of other holders. In the event that the proposed method of disposition specified by the Initiating Investor shall be an underwritten public offering, (i) the managing underwriter shall be selected by such Investor (which selection, in the case of Morgan Stanley, shall be subject to the approval of the Company, which approval shall not be unreasonably withheld, conditioned or delayed); and (ii) the number of shares of Registrable Stock to be included in such an offering may be reduced if and to the extent that, in the good faith opinion of the managing underwriter of such offering, inclusion of all shares would adversely affect the marketing (including the offering price) of the Registrable Stock to be sold, and, in the case of any such reduction, shares shall be included in such offering to the extent so permissible on the following basis: (A) first, all Registrable Stock proposed to be included by the Investors shall be included (subject to pro rata reduction among the Investors seeking to include Registrable Stock in such offering based on the number of such shares of Registrable Stock held by the Investors) and (B) second, to the extent provided above, Common Stock proposed to be included by the Company for the account of the Company or other stockholders of the Company shall be included. The Company shall abandon any Demand Registration upon the request of the Initiating Investor and neither the Company nor such Investor shall have any liability to any Investor with respect to such abandonment. Notwithstanding anything else to the contrary contained herein, (i) the Company shall not be required to effect more than two Demand Registrations at the request of WCAS or more than two Demand Registrations at the request of Morgan Stanley, in each case, under this Section 2(a) on

Form S-1 or any successor thereto, and (ii) the Company shall not be required to effect a Demand Registration hereunder unless (x) in the case of a registration on Form S-1 or any successor thereto, the reasonably anticipated aggregate net proceeds thereof (determined at the time of the giving of the Demand Request) exceed $25,000,000, or (y) in the case of a registration on Form S-3 or any successor thereto, such Demand Registration relates to the registration of at least 1,000,000 shares of Registrable Stock (as adjusted for any stock splits, stock dividends, stock combinations and similar events occurring after the date hereof), in each case, determined at the time of the giving of the Demand Request. Notwithstanding anything to the contrary herein, each of WCAS and Morgan Stanley shall have the right to make an unlimited number of Demand Requests on Form S-3 or any successor thereto; provided, however, that the Company shall not be required to effect more than two Demand Registrations in any twelve-month period under this Section 2(a) on Form S-3 or any successor thereto.

(b) Short-Form Registration Qualification. From and after the IPO Date, the Company shall use its commercially reasonable efforts to qualify under the provisions of the Securities Act, and thereafter, to continue to qualify at all times, for registration on Form S-3 or any successor thereto. In the event the Company fails to so qualify, the Company shall be required to effect Demand Registrations on Form S-1 or any successor thereto to the same extent as the Company would be required to effect Demand Registrations on Form S-3 or any successor thereto.

(c) Certain Provisions Relating to Demand Registrations. In connection with a Demand Registration, the Company shall be obligated to effect such Demand Registration in accordance with the following provisions:

(i) the obligations of the Company under Section 2(a) above to effect a Demand Registration shall be deemed satisfied only when a registration statement covering all of the shares of Registrable Stock specified in the applicable Demand Request and in each notice delivered by any other Investor requesting registration of Registrable Stock in response to the Demand Registration Notice for sale in accordance with the intended method of disposition specified by Initiating Investor in the Demand Request shall have become effective and remained effective through the end of the period of distribution of the registration contemplated thereby (determined as provided in the last paragraph of Section 2(f)); provided, however, that in the case of the initial Demand Registration in which the proposed method of disposition specified by the Initiating Investor is an underwritten public offering on Form S-1, the obligations of the Company under Section 2(a) shall nevertheless be deemed satisfied if the number of shares to be included in the offering by the Initiating Investor is reduced by not more than 20% because in good faith opinion of the managing underwriter of such proposed offering inclusion of all shares requested by such Investor to be included in the offering would adversely affect the marketing (including the offering price) of the Registrable Stock to be sold; and

(ii) Without the consent of the Initiating Investor, which will not be unreasonably withheld, the Company will not effect any registration of its Common Stock, whether for its own account or that of other holders, from the date of receipt of a Demand Request in which the proposed method of disposition specified by the Initiating

Investor is an underwritten public offering until the completion of the period of distribution (determined as provided in the last paragraph of Section 2(f)) of the Registrable Stock covered by the registration statement filed pursuant to such Demand Request.

(d) Piggyback Registration Rights. If at any time the Company proposes to register any of its Common Stock or any other equity securities (or other securities convertible into equity securities) of the Company under the Securities Act for sale to the public, whether for its own account or for the account of other security holders or both (other than a Demand Registration, or a registration on Form S-4 or Form S-8 promulgated under the Securities Act (or any successor forms thereto) or any other form not available for registering the Registrable Stock for sale to the public), as soon as practicable prior to the filing of such registration statement with the Commission, it will give written notice of its intention to effect such registration (each such notice a “Piggyback Notice”) to (i) if such proposed registration is being made in connection with the Company’s initial Public Offering, WCAS and Morgan Stanley and, unless WCAS and Morgan Stanley elect to waive their rights under this Section 2(d) as provided below with respect to such registration within twenty business days of receiving its Piggyback Notice, to each other Investor or (ii) if such proposed registration is to occur after the IPO Date, to each Investor. Upon the written request of any Investor, given within 20 days after the giving of the Piggyback Notice to all Investors, to register any of its Registrable Stock (which request shall state the number of shares of Registrable Stock to be so registered and the intended method of disposition thereof), the Company will use its commercially reasonable efforts to cause the Registrable Stock, as to which registration shall have been so requested, to be included in the securities to be covered by the registration statement proposed to be filed by the Company, all to the extent required to permit the sale or other disposition by such Investor of such Registrable Stock so registered; provided, that nothing herein shall prevent the Company from abandoning or delaying such registration at any time; provided, however, that the expenses of such withdrawn registration shall be borne by the Company in accordance with Section 2(i) hereof. Notwithstanding anything to the contrary contained herein, in connection with any registration statement to be filed prior to the IPO Date, if WCAS and Morgan Stanley elect to waive their rights under this Section 2(d) with respect to such registration and the related initial Public Offering, such waiver shall be effective as a waiver of the rights of all Investors under this Section 2(d) with respect to such registration and offering. In the event that any registration referred to in this Section 2(d) shall be, in whole or in part, an underwritten public offering, such Registrable Stock shall be included in the underwriting on the same terms and conditions as the shares otherwise being sold through underwriters under such registration. The number of shares of Registrable Stock to be included in such an underwritten offering may be reduced if and to the extent that, in the good faith opinion of the managing underwriter of such offering, inclusion of all shares would adversely affect the marketing (including the offering price) of the shares to be sold, and, in the case of any such reduction, shares shall be included in such offering to the extent so permissible on the following basis: (A) first, all shares proposed to be included by the Company for the account of the Company shall be included, (B) second, all Registrable Stock proposed to be included by the Investors shall be included (subject to pro rata reduction among the Investors seeking to include Registrable Stock in such offering based on the number of such shares of Registrable Stock held by the Investors), and (C) finally, Common Stock proposed to be included by the Company for the account of other stockholders of the Company shall be included.

(e) Holdback Agreement. Notwithstanding anything to the contrary contained in this Agreement, with respect to any underwritten Public Offering by the Company, upon request of the managing underwriter of such offering, each Investor shall refrain from selling or otherwise transferring Registrable Stock (other than pursuant to Section 2(a) or 2(d) above) during the period beginning no earlier than the tenth day preceding the effective date of the registration statement for such offering and continuing through (i) in the case of the Company’s initial Public Offering, the end of the period of distribution of the registration contemplated thereby but such period not to exceed 180 days after the IPO Date or (ii) in case of any other Public Offering, the end of the period of distribution of the registration contemplated thereby but such period not to exceed 90 days after the shares are first sold to the public in such offering and, if requested by any managing underwriter of such offering, to execute a customary lock-up agreement. The foregoing provisions of this Section 2(e) shall only be applicable to each Investor if all other Persons with registration rights (whether or not pursuant to this Agreement) and all officers, directors and holders of more than 1% of the then outstanding Common Stock of the Company enter into similar agreements. The provisions of this Section 2(e) shall terminate upon the earlier to occur of (i) the second anniversary of the IPO Date and (y) WCAS giving written notice of such termination to the Company (a copy thereof to be promptly forwarded by the Company to the other Investors).

(f) Certain Registration Procedures. If and whenever the Company is required by the provisions of this Section 2 to use its commercially reasonable efforts to effect the registration of Registrable Stock under the Securities Act, the Company will, as expeditiously as possible:

(i) (x) prepare (and afford the Investors Counsel (as hereinafter defined) reasonable opportunity to review and comment thereon) and file with the Commission a registration statement with respect to such securities (A) in case of a Demand Registration on Form S-1 or any successor thereto, no later than 120 calendar days after the date of the applicable Demand Request and (B) in the case of a Demand Registration on Form S-3 or any successor thereto, no later than 45 calendar days after the applicable Demand Request, and (y) use its commercially reasonable efforts to cause such registration statement to become effective (A) in case of a Demand Registration on Form S-1 or any successor thereto, no later than 150 calendar days after the date such registration statement is filed with the SEC and (B) in the case of a Demand Registration on Form S-3 or any successor thereto, no later than 75 calendar days after the date such registration statement is filed with the SEC, and (z) use its commercially reasonable efforts to cause such registration statement to remain effective (A) in the case of a Demand Registration on Form S-1 or any successor thereto, until the earlier of (1) the date on which all Registrable Stock registered pursuant to such registration statement shall have been sold to the public and (2) the date which is 180 calendar days after the date on which such registration statement is declared effective by the SEC and (B) in the case of a Demand Registration on Form S-3 or any successor thereto, until the earlier of (1) the second anniversary of the effective date of such registration statement and (2) the date on which all of the Registrable Stock requested to be registered by the Investors is no longer considered Registrable Stock;

(ii) prepare (and afford the Investors Counsel reasonable opportunity to review and comment thereon) and file with the Commission such amendments and supplements to such registration statement and the prospectus used in connection therewith as may be necessary to keep such registration statement effective through the end of period of distribution contemplated thereby (determined as provided in the last paragraph of Section 2(f)) and comply with the provisions of the Securities Act with respect to the disposition of all Registrable Stock covered by such registration statement in accordance with the selling Investors’ intended method of disposition set forth in such registration statement through the end of such period of distribution;

(iii) furnish to each selling Investor and to each underwriter such number of copies of the registration statement and the prospectus included therein (including each preliminary prospectus) as such persons may reasonably request in order to facilitate the public sale or other disposition of the Registrable Stock covered by such registration statement;

(iv) use its commercially reasonable efforts to register or qualify the Registrable Stock covered by such registration statement under the securities or blue sky laws of such jurisdictions as WCAS, any other Initiating Investor, the Investors Counsel or, in the case of an underwritten public offering, the managing underwriter, shall reasonably request; provided, that the Company will not be required to (x) qualify generally to do business in any jurisdiction where it would not otherwise be required to qualify but for this Section 2(f)(iv), (y) subject itself to taxation in any such jurisdiction in which it would not otherwise be subject to taxation but for this Section 2(f)(iv) or (z) consent to general service of process in any jurisdiction in which it would not otherwise be subject to general service of process but for this Section 2(f)(iv);

(v) immediately notify each selling Investor under such registration statement and each underwriter, at any time when a prospectus relating thereto is required to be delivered under the Securities Act, of the happening of any event as a result of which the prospectus contained in such registration statement, as then in effect, includes an untrue statement of a material fact or omits to state any material fact required to be stated therein or necessary to make the statements therein not misleading in light of the circumstances then existing (and upon receipt of any such notice, each selling Investor agrees to suspend sales of Registrable Stock covered by such prospectus until such time as the Company notifies it that the prospectus (as supplemented or amended) no longer includes any untrue statement of a material fact or omits to state any material fact required to be stated therein or necessary to make the statements therein not misleading in light of the circumstances then existing) and use its commercially reasonable efforts to promptly prepare and file with the SEC a supplement or amendment to the registration statement or other appropriate filing with the SEC to correct such untrue statement or omission, and deliver a number of copies of such supplement or amendment to each Investor selling Registrable Stock pursuant to such registration statement as such Investor may reasonably request;

(vi) use its commercially reasonable efforts (if the offering is underwritten) to furnish, at the request of WCAS, any other Initiating Investor or the Investors Counsel,

on the date that Registrable Stock is delivered to the underwriters for sale pursuant to such registration: (A) an opinion, dated such date, of counsel representing the Company for the purposes of such registration, addressed to the underwriters and to each selling Investor, stating that such registration statement has become effective under the Securities Act and that (1) to the best knowledge of such counsel, no stop order suspending the effectiveness thereof has been issued and no proceedings for that purpose have been instituted or are pending or contemplated under the Securities Act, (2) the registration statement, the related prospectus, and each amendment or supplement thereof, comply as to form in all material respects with the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder (except that such counsel need express no opinion as to financial statements, the notes thereto, and the financial schedules and other financial and statistical data contained therein) and (3) to such other effects as may reasonably be requested by counsel for the underwriters or by WCAS, any other Initiating Investor or the Investors Counsel, and (B) a letter dated such date from the independent public accountants retained by the Company, addressed to the underwriters, stating that they are independent public accountants within the meaning of the Securities Act and that, in the opinion of such accountants, the financial statements of the Company included in the registration statement or the prospectus, or any amendment or supplement thereof, comply as to form in all material respects with the applicable accounting requirements of the Securities Act, and such letter shall additionally cover such other financial matters (including information as to the period ending no more than five business days prior to the date of such letter) with respect to the registration in respect of which such letter is being given as such underwriters, WCAS, any other Initiating Investor or the Investors Counsel may reasonably request;

(vii) make available for inspection by WCAS, any other Initiating Investor, any underwriter participating in any distribution pursuant to such registration statement, the Investors Counsel and any accountant or other agent retained by one ore more of such parties, all financial and other records, pertinent corporate documents and properties of the Company, and cause the Company’s officers, directors and employees to supply all information reasonably requested by WCAS, any other Initiating Investor, the Investors Counsel or any of such underwriters, attorneys, accountants or agents in connection with such registration statement and permit WCAS, any other Initiating Investor, the Investors Counsel and such underwriters, attorneys, accountants or agents to participate in the preparation of such registration statement;

(viii) use its commercially reasonable efforts to list all the Registrable Stock covered by such registration statement on the New York Stock Exchange or the Nasdaq Global Select Market; and

(ix) make available to each Investor, as soon as reasonably practicable, an earnings statement covering the period of at least 12 months, but not more than 18 months, beginning with the first month of the first fiscal quarter after the effective date of such registration statement, which earnings statement shall satisfy the provisions of Section 11(a) of the Securities Act, including, without limitation, Rule 158 promulgated thereunder.

For purposes of Sections 2(c), 2(e) and 2(f)(ii) above, and subject to Section 2(f)(i), the “period of distribution” of Registrable Stock in an underwritten public offering shall be deemed to extend until each underwriter has completed the distribution of all securities purchased by it, and the period of distribution of Registrable Stock in any other registration shall be deemed to extend until the sale of all Registrable Stock covered thereby.

(g) Information From Selling Investors. In connection with each registration hereunder, Investors selling Registrable Stock will furnish to the Company in writing such information with respect to themselves and the proposed distribution by them as shall be reasonably necessary in order to assure compliance with federal and applicable state securities laws.

(h) Underwriting Agreement. In connection with any registration pursuant to this Section 2 that covers an underwritten public offering, the Company and Investors selling Registrable Stock each agree to enter into a written agreement with the managing underwriter selected in the manner herein provided in such form and containing such provisions as are customary in the securities business for such an arrangement between major underwriters, selling stockholders and a company of the Company’s size and investment stature; provided, that in the case of any Demand Registration, such agreement shall be satisfactory to WCAS and any other Initiating Investor.

(i) Expenses. The Company will pay all Registration Expenses (as defined below) incurred in complying with Section 2 of this Agreement. All Selling Expenses (as defined below) incurred in connection with any registered offering of securities that, pursuant to this Section 2, includes Registrable Stock, shall be borne by the participating sellers in proportion to the number of shares sold by each, or by such persons, including the Company if the Company is a seller, as they may agree. All expenses incident to performance of or compliance by the Company with Section 2 hereof, including, without limitation, all Commission, stock exchange, Nasdaq or National Association of Securities Dealers, Inc. (“NASD”) registration and filing fees (including, without limitation, fees and expenses incurred in connection with the listing of the Common Stock of the Company on any securities exchange or exchanges or Nasdaq), printing, distribution and related expenses, fees and disbursements of counsel and independent public accountants for the Company, all reasonable fees and disbursements of one firm counsel for the participating sellers selected by WCAS and, in the case of a Demand Registration, any other Initiating Investor (or, in the event that WCAS is not participating in such registration and such registration is not Demand Registration, such counsel shall be selected by the Investors holding a majority of the Shares of Registrable Stock proposed to be included in such registration) (the “Investors Counsel”), all fees and expenses incurred in connection with compliance with state securities or blue sky laws and the rules of the NASD or any securities exchange, transfer taxes and fees of transfer agents and registrars, but excluding any Selling Expenses, are herein called “Registration Expenses”. All underwriting discounts and selling commissions applicable to the sale of Registrable Stock are herein called “Selling Expenses”.

(j) Deferral; Suspension. Notwithstanding anything herein to the contrary, the Company may defer the filing (but not the preparation) of a registration statement with respect to any Demand Registration or suspend the rights of selling Investors to make sales

pursuant to a registration statement otherwise required to be kept effective hereunder if the Company determines in good faith that there exists a material proposed transaction (including any proposed acquisition or disposition) or other material non-public information, in each case, that would be required to be disclosed in such registration statement and the disclosure of which would either have a material adverse effect on such material proposed transaction or the Company; provided, that such delay shall not continue beyond the earlier of (A) the date upon which such material information is otherwise disclosed to the public or ceases to be material and (B) 90 days after the Company effects such deferral or suspension; provided, further that, in the case of any Demand Registration, the time periods set forth in Section 2(f)(i) shall be tolled for the period of such deferral or suspension.

SECTION 3. Indemnification Rights and Obligations In Respect of Registered Offerings of Registrable Stock.

(a) Company Indemnification of Selling Investors. In the event of a registration of any of the Registrable Stock under the Securities Act pursuant to Section 2 of this Agreement, the Company will indemnify and hold harmless each seller of Registrable Stock thereunder and each other person, if any, who controls such seller within the meaning of the Securities Act and each underwriter and each person who controls any underwriter within the meaning of the Securities Act, against any losses, claims, damages or liabilities, joint or several, (or actions in respect thereof) to which such seller, underwriter or controlling person may become subject under the Securities Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) (i) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in any registration statement under which such Registrable Stock was registered under the Securities Act, any preliminary prospectus or final prospectus contained therein, or any amendment or supplement thereof, or arise out of or are based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading or (ii) arise out of or are based on any violation or alleged violation by the Company of the Securities Act, the Exchange Act, any state securities law or any rule or regulation promulgated under the Securities Act, the Exchange Act or any state securities law and will reimburse each such seller, each such underwriter and each such controlling person for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, liability or action; provided, that the Company will not be liable in any such case if and to the extent that any such loss, claim, damage, liability or action arises out of or is based upon an untrue statement or alleged untrue statement or omission or alleged omission so made in strict conformity with information furnished by such seller, such underwriter or such controlling person in writing specifically for use in such registration statement or prospectus; provided, further, that the indemnity agreement contained in this Section 3(a) shall not apply to amounts paid in settlement of any such loss, claim, damage, liability, or action if such settlement is effected without the consent of the Company (which consent shall not be unreasonably withheld).

(b) Selling Investor Indemnification of the Company and the Other Selling Stockholders. In the event of a registration of any of the Registrable Stock under the Securities Act pursuant to Section 2 of this Agreement, each seller of such Registrable Stock thereunder, severally and not jointly, will indemnify and hold harmless the Company and each person, if any,

who controls the Company within the meaning of the Securities Act, each officer of the Company who signs the registration statement, each director of the Company, each underwriter and each person who controls any underwriter within the meaning of the Securities Act, and each other seller of Registrable Stock and each person who controls any such other seller of Registrable Stock, against all losses, claims, damages or liabilities, joint or several, (or actions in respect thereof) to which the Company or such officer or director or underwriter or other seller or controlling person may become subject under the Securities Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in the registration statement under which such Registrable Stock was registered under the Securities Act, any preliminary prospectus or final prospectus contained therein, or any amendment or supplement thereof, or arise out of or are based upon the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, and will reimburse the Company and each such officer, director, underwriter, other seller of Registrable Stock and controlling person for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, liability or action; provided, that such seller will be liable hereunder in any such case if and only to the extent that any such loss, claim, damage, liability or action arises out of or is based upon an untrue statement or alleged untrue statement or omission or alleged omission made in reliance upon and in strict conformity with information pertaining to such seller, as such, furnished in writing to the Company by such seller specifically for use in such registration statement or prospectus; provided, further, that the aggregate liability of each seller hereunder shall be limited to the proceeds (net of underwriting discounts and commissions) received by such seller from the sale of Registrable Stock covered by such registration statement; provided, further, that the indemnity agreement contained in this Section 3(b) shall not apply to amounts paid in settlement of any such loss, claim, damage, liability, or action if such settlement is effected without the consent of such seller of Registrable Stock (which consent shall not be unreasonably withheld).

(c) Indemnification Procedures. Promptly after receipt by an indemnified party hereunder of notice of the commencement of any action, such indemnified party shall, if a claim in respect thereof is to be made against the indemnifying party hereunder, notify the indemnifying party in writing thereof, but the omission so to promptly notify the indemnifying party shall not relieve it from any liability which it may have to any indemnified party other than under this Section 3. In case any such action shall be brought against any indemnified party and it shall promptly notify the indemnifying party of the commencement thereof, the indemnifying party shall be entitled to participate in and, to the extent it shall wish, to assume and undertake the defense thereof with counsel reasonably satisfactory to such indemnified party, and, after notice from the indemnifying party to such indemnified party of its election so to assume and undertake the defense thereof, the indemnifying party shall not be liable to such indemnified party under this Section 3 for any legal expenses subsequently incurred by such indemnified party in connection with the defense thereof other than reasonable costs of investigation and of liaison with counsel so selected; provided, that if the defendants in any such action include both the indemnified party and the indemnifying party and the indemnified party shall have reasonably concluded that there may be reasonable defenses available to it which are different from or additional to those available to the indemnifying party, or if the interests of the indemnified party reasonably may be deemed to conflict with the interests of the indemnifying party, the indemnified party shall have the right to select a separate counsel and to assume such

legal defenses and otherwise to participate in the defense of such action, with the reasonable expenses and fees of such separate counsel and other expenses related to such participation to be reimbursed by the indemnifying party as incurred. Notwithstanding the foregoing, any indemnified party shall have the right to retain its own counsel in any such action, but the fees and disbursements of such counsel shall be at the expense of such indemnified party; provided that such fees and expenses shall be at the expense of the indemnifying party if (i) the indemnifying party shall have failed to retain counsel for the indemnified person as aforesaid or (ii) the indemnifying party and such indemnified party shall have mutually agreed to the retention of such counsel. It is understood that the indemnifying party shall not, in connection with any action or related actions in the same jurisdiction, be liable for the fees and disbursements of more than one separate firm qualified in such jurisdiction to act as counsel for the indemnified party. No indemnifying party, in the defense of any such claim or litigation, shall, except with the consent of such indemnified party, which consent shall not be unreasonably withheld, consent to entry of any judgment or enter into any settlement of any pending or threatened action in respect of which any indemnified party is or could have been a party and indemnity was sought hereunder by such indemnified party unless such judgment or settlement includes as an unconditional term thereof the giving by the claimant or plaintiff to such indemnified party of a release from all liability in respect to such claim or litigation. The indemnification of underwriters provided for in this Section 3 shall be on such other terms and conditions as are at the time customary and reasonably required by such underwriters as provided in Section 2(h).

(d) Contribution. If the indemnification provided for in Sections 3(a) and 3(b) above is unavailable or insufficient to hold harmless an indemnified party under such Sections in respect of any losses, claims, damages or liabilities or actions in respect thereof referred to therein, then each indemnifying party shall in lieu of indemnifying such indemnified party contribute to the amount paid or payable by such indemnified party as a result of such losses, claims, damages, liabilities or actions in such proportion as appropriate to reflect the relative fault of the Company, on the one hand, and the underwriters or the sellers of such Registrable Stock, on the other, in connection with the statements or omissions which resulted in such losses, claims, damages, liabilities or actions as well as any other relevant equitable considerations, including, without limitation, the failure to give any notice under Section 3(c) above. The relative fault shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact relates to information supplied by the Company, on the one hand, or the underwriters or the sellers of such Registrable Stock, on the other, and to the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission. The Company and each of the Investors agrees that it would not be just and equitable if contributions pursuant to this Section were determined by pro rata allocation (even if all of the sellers of such Registrable Stock were treated as one entity for such purpose) or by any other method of allocation which did not take account of the equitable considerations referred to above in this Section. The amount paid or payable by an indemnified party as a result of the losses, claims, damages, liabilities or action in respect thereof, referred to above in this Section, shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any such action or claim. Notwithstanding the provisions of this Section, the sellers of such Registrable Stock shall not be required to contribute any amount, in the aggregate, in excess of the amount, if any, by which the total price at which the Registrable Stock sold by each of them was offered to the public exceeds the amount of any

damages which they are otherwise required to pay by reason of such untrue or alleged untrue statement or omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act), shall be entitled to contribution from any person who is not guilty of such fraudulent misrepresentation.

SECTION 4. Rule 144. The Company agrees with the Investors that, from and after the IPO Date, it shall timely file any and all reports required to be filed by it under the Securities Act and the Exchange Act and the rules and regulations adopted by the Commission thereunder, or, if the Company is not thereafter required to file any such reports, it shall, upon the written request of any Investor, make publicly available at all times after 90 calendar days following the IPO Date such information as is necessary to permit sales pursuant to Rule 144 under the Securities Act. Upon the written request of any Investor, the Company shall promptly furnish to such Investor a written statement by the Company as to its compliance with the reporting requirements as set forth in this Section 4 and such other information as may be reasonably requested in availing any Investor of any rule or regulation of the SEC which permits the sellers of any such securities without registration.

SECTION 5. Duration of Agreement. Except as provided in Section 2(e), all provisions of this Agreement shall survive so long as any Investor owns any Registrable Stock.

SECTION 6. Miscellaneous.

(a) Additional Registration Rights. Without the consent of WCAS, the Company shall not grant any registration rights to any other person that are inconsistent or conflict with the registration rights granted hereunder.

(b) Headings. Headings of sections of this Agreement are inserted for convenience of reference only and shall not affect the interpretation hereof.

(c) Severability. Each provision of this Agreement shall be treated as a separate and independent clause, and the unenforceability of any one clause shall in no way impair the enforceability of any of the other clauses contained herein. If one or more of the provisions contained in this Agreement shall for any reason be held to be unenforceable, such provision or provisions shall be construed by the appropriate judicial body by limiting or reducing it or them, so as to be enforceable to the maximum extent compatible with applicable law, and no other provision hereof shall be affected by such holding, limitation or reduction.

(d) Benefits of Agreement. This Agreement shall inure to the benefit of and be binding upon the parties hereto and their respective successors and permitted assigns and nothing in this Agreement, expressed or implied, is intended to confer on any person other than the parties hereto, their respective successors and permitted assigns, any rights, remedies, obligations or liabilities under or by reason of this Agreement. The rights and obligations of the parties hereto shall not be assigned without the consent of WCAS, in the case of any assignment by the Company, or the Company, in the case of any assignment by any Investor, and any attempted assignment in violation of this Section 6(d) shall be null and void; provided, that without the prior written consent of WCAS and the Company, any Investor’s rights and obligations hereunder are assignable to a transferee in connection with any transfer of

Registrable Stock (including by means of transferring securities that are directly or indirectly convertible into or exercisable or exchangeable for Registrable Stock) so long as (i) such transferee expressly agrees in writing to become bound hereby as an “Investor” hereunder and (ii) notice of such transfer is given to the Company and WCAS.

(e) Entire Agreement; Modification. This Agreement constitutes the entire agreement among the parties with respect to the subject matter hereof and supercedes all prior agreements and understandings, oral and written, between the parties hereto with respect to the subject matter hereof. This Agreement may not be modified or amended except by a writing signed by the Company and WCAS; provided, that no provision of this Agreement may be modified or amended in a manner materially adverse to an Investor other than WCAS (in its capacity as an Investor hereunder) if such modification or amendment affects such Investor disproportionately relative to the other Investors except with the written consent of such Investor; provided, further, that no provision of this Agreement may be modified, waived or amended in a manner adverse to Morgan Stanley or any of its successors or assignees who become a party to this Agreement in accordance with the terms hereof (collectively, the “Morgan Stanley Investors”) except with the prior written consent of the holders of a majority of Registrable Stock held by the Morgan Stanley Investors (such consent not to be unreasonably withheld or delayed); provided, further, however, that notwithstanding the foregoing, in accordance with the last sentence of Section 6(d) above or upon the written agreement of the Company and WCAS, additional Investors may be added to this Agreement (it being understood that any amendment of the provisions of this Agreement in connection with the addition of new Investors to this Agreement does not require the prior written consent of the Morgan Stanley Investors so long as no provision of this Agreement is amended in a manner adverse to any of the Morgan Stanley Investors). Except as otherwise provided herein, any waiver of any provision of this Agreement must be in a writing signed by the party against whom enforcement of such waiver is sought.

(f) Notices. All notices, requests, instructions and other documents that are required to be or may be given or delivered pursuant to the terms of this Agreement shall be in writing and shall be sufficient in all respects if delivered by hand or national overnight courier service, transmitted by facsimile (subject to confirmation by return facsimile of such facsimile transmission) or mailed by registered or certified mail, postage prepaid, as follows:

If to the Company, to it at:

16825 Northchase Drive

Houston, Texas 77060

Facsimile: (832) 601-6688

Attention: Chief Executive Officer

with a copy to:

Welsh, Carson, Anderson & Stowe IX, L.P.

320 Park Avenue, Suite 2500

New York, New York 10022

Attention: D. Scott Mackesy

Facsimile: (212) 893-9566

with an additional copy to:

Ropes & Gray LLP

45 Rockefeller Plaza

New York, New York 10111

Attention: Othon A. Prounis, Esq.

Facsimile: (212) 841-5725

If to any Investor, to such Investor at its address set forth on Schedule I;

or such other address or addresses as any party hereto shall have designated by notice in writing to the other parties hereto. Such notices, requests, instructions and other documents shall be deemed given or received (i) five business days following sending by registered or certified mail, postage prepaid, (ii) one business day following sending by national overnight courier service, (iii) the day of sending, if sent by facsimile prior to 5:00 p.m. (EST) on any business day or the next succeeding business day if sent by facsimile after 5:00 p.m. (EST) on any business day or on any day other than a business day or (iv) when delivered, if delivered by hand.

(g) Counterparts. This Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. Any or all such counterparts may be executed by facsimile.

(h) Changes in Registrable Stock. If, and as often as, there are any changes in the Registrable Stock by way of stock split, stock dividend, combination or reclassification, or through merger, consolidation, reorganization or recapitalization, or by any other means, appropriate adjustment shall be made in the provisions hereof as may be required so that the rights and privileges granted hereby shall continue with respect to the Registrable Stock as so changed and the Company shall make appropriate provision in connection with any merger, consolidation, reorganization or recapitalization that any successor to the Company (or resulting parent thereof) shall agree, as a condition to the consummation of any such transaction, to expressly assume the Company’s obligations hereunder.

(i) Specific Performance. Each party hereto agrees that a remedy at law for any breach or threatened breach by such party of this Agreement would be inadequate and therefore agrees that any other party hereto shall be entitled to specific performance of this Agreement in addition to any other available rights and remedies in case of any such breach or threatened breach.

(j) Governing Law. This Agreement and all disputes arising out of or relating to this Agreement, its subject matter, the performance by the parties of their respective obligations hereunder or the claimed breach hereof, whether in tort, contract or otherwise, shall be governed by and construed in accordance with the internal laws of the State of New York.

(k) Interpretation. As used herein, the words “hereof”, “herein”, “herewith” and words of similar import shall, unless otherwise stated, be construed to refer to this

Agreement as a whole and not to any particular provision of this Agreement, and the word “Section” refers to a Section of this Agreement unless otherwise specified. Whenever the words “include”, “includes” or “including” are used in this Agreement they shall be deemed to be followed by the words “without limitation”. The definitions contained in this Agreement are applicable to the singular as well as the plural forms of such terms and to the masculine as well as to the feminine and neuter genders of such terms.

[SIGNATURE PAGES FOLLOW]

IN WITNESS WHEREOF, each of the parties hereto has duly executed and delivered this Registration Rights Agreement as of the date first written above.

THE COMPANY:

US ONCOLOGY HOLDINGS, INC.

By:

Name:

Title:

WCAS:

WELSH, CARSON, ANDERSON & STOWE IX, L.P.
By:	WCAS IX Associates LLC, its General Partner
By:
Name:
Title:

MORGAN STANLEY:

MORGAN STANLEY STRATEGIC
INVESTMENTS, INC.

By:

Name:

Title:

OTHER INVESTORS:

WCAS MANAGEMENT CORPORATION

By:

Name:

Title:

Russell L. Carson

Bruce K. Anderson

Thomas E. McInerney

Robert A. Minicucci

Anthony J. de Nicola

Paul B. Queally

D. Scott Mackesy

D. Scott Mackesy – IRA
Charles Schwab & Co., Inc. Custodian

Sanjay Swani

John D. Clark – IRA
Charles Schwab & Co., Inc. Custodian

John D. Clark

James R. Matthews – IRA
Charles Schwab & Co., Inc. Custodian

Jonathan M. Rather – IRA
Charles Schwab & Co., Inc. Custodian

Sean M. Traynor

John Almeida

Rona Drogy

Dave Mintz

Clinton Biondo

Ankar Kumar

Michael E. Donovan

Brian Regan

Eric J. Lee

By:
Name:	Jonathan M. Rather
Title:	Attorney-in-Fact

THE PATRICK WELSH 2004
IRREVOCABLE TRUST

By:

Name:

Title:

R. Dale Ross

Lloyd K. Everson, M.D.

Phillip H. Watts

Bruce D. Broussard

George D. Morgan

Leo E. Sands

Atul Dhir, M.B.B.S., D. Phil

ROSS RESOURCES LIMITED

By:

Name:

Title:

Schedule I to Amended and Restated Registration Rights Agreement

Investors

Address for Notices

Welsh, Carson, Anderson & Stowe IX, L.P. WCAS Management Corporation Russell L. Carson Bruce K. Anderson The Patrick Welsh 2004 Irrevocable Trust Thomas E. McInerney Robert A. Minicucci Anthony J. de Nicola Paul B. Queally D. Scott Mackesy Sanjay Swani John D. Clark IRA f/b/o John D. Clark IRA f/b/o D. Scott Mackesy IRA f/b/o James R. Matthews IRA f/b/o Jonathan M. Rather Sean M. Traynor John Almedia, Jr. Stacey Bellet* Suzanne Bellet Price* Rona Drogy David Mintz Clinton M. Biondo Ankur Kumar Michael E. Donovan Brian T. Regan Eric J. Lee Jill A. Hanau

c/o Welsh, Carson, Anderson & Stowe 320 Park Avenue, Suite 2500 New York, New York 10022 Attention: D. Scott Mackesy Facsimile: (212) 893-9566

* Additional copy to:

125 East 72nd Street

Apt. 11-D

New York, NY 10021

Attention: David F. Bellet

Robert A. Ortenzio Rocco A. Ortenzio c/o Select Capital Corporation 4718 Old Gettysburg Road, Suite 405 Mechanicsburg, PA 17055 Attention: Robert Nause Facsimile: (717) 972-1080

SCHEDULE 1 TO AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT

Investors	Address for Notices
Melkus Partners Melkus Family Foundation The Lauren Evelyn Melkus Trust Lauren Melkus	c/o Kenneth J. Melkus 102 Woodmont Blvd., Suite 110 Nashville, TN 37203 Facsimile: (615) 383-0104
Joelle M. Kayden	c/o Accolade Partners, L.P. 7900 Westpark Drive, Suite T-602 McLean, VA 22102 Facsimile: (703) 749-7800
Weigers & Co. LLC Betsy Weigers 2002 Unit Trust George A. Weigers 2001 Unit Trust	c/o Weigers Capital Management, LLC 55 Madison Street, Suite 680 Denver, CO 80206
Kyle M. Fink, M.D.	PBM 391 0105 Edwards Village Blvd., C104 Edwards, CO 81632
Texas Oncology, P.A.	c/o R. Steven Paulson, M.D. 12221 Merit Drive, Suite 500 Dallas, TX 75251
R. Dale Ross Lloyd K. Everson, M.D. Phillip H. Watts Bruce D. Broussard George D. Morgan Leo E. Sands Atul Dhir, M.B.B.S., D. Phil Ross Resources Limited Richard J. Hall	c/o US Oncology, Inc. 16825 Northchase Drive Houston, TX 77060 Attention: R. Dale Ross Facsimile: (832) 601-6688
California State Teachers’ Retirement System	7667 Folsom Boulevard, Suite 250 Sacramento, CA 95826 Attention: Real Desrochers and Seth Hall Facsimile: (916) 229 3790
Gunners Investment Pte Ltd.	c/o GIC Special Investments Pte Ltd. 255 Shoreline Drive, Suite 600 Redwood City, CA 94065 Attention: Andrew Kwee Facsimile: (650) 802-1213

SCHEDULE 1 TO AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT

Investors	Address for Notices
Abu Dhabi Investment Authority	P.O. Box 3600 Corniche Street Abu Dhabi United Arab Emirates Attention: Abubaker Al Khouri Facsimile: (971 2) 626-4616
A.S.F. Co-Investment Partners II, L.P.	c/o IBM Retirement Funds 3001 Summer Street, MD 49 Stamford, CT 06905 Attention: Betty Sheets Facsimile: (203) 316-2190 With a copy to: c/o Portfolio Advisors, LLC 9 Old Kings Highway South Darien, CT 06820 Attention: Hugh Perloff Facsimile: (203) 662-0013

SCHEDULE 1 TO AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT

EX-10.4

Exhibit 10.4

EXECUTION COPY

AMENDMENT NO. 4 (this “Amendment”) dated as of December 21, 2006, among US ONCOLOGY HOLDINGS, INC., a Delaware corporation (“Holdings”), US ONCOLOGY, INC., a Delaware corporation (the “Borrower”), the Subsidiary Loan Parties (as defined in the Credit Agreement (as defined below)) party hereto, the LENDERS party hereto and JPMORGAN CHASE BANK, N.A., as Administrative Agent.

A. Pursuant to the Credit Agreement dated as of August 20, 2004, as amended as of March 17, 2005, November 15, 2005, and July 10, 2006 (the “Credit Agreement”), among Holdings, the Borrower, the Lenders party thereto, JPMorgan Chase Bank, N.A., as Administrative Agent and Collateral Agent, Wachovia Bank, National Association, as Syndication Agent, and Citicorp North America, Inc., as Documentation Agent, the Lenders and the Issuing Banks (such terms and each other capitalized term used but not defined herein having the meaning assigned to each such term in the Credit Agreement (as amended hereby)) have extended credit to the Borrower, and have agreed to extend credit to the Borrower, in each case pursuant to the terms and subject to the conditions set forth therein.

B. The Borrower has requested that the Lenders agree to amend certain provisions of the Credit Agreement and the Collateral Agreement as set forth herein.

C. The undersigned Lenders are willing so to amend the Credit Agreement and the Collateral Agreement pursuant to the terms and subject to the conditions set forth herein.

Accordingly, in consideration of the mutual agreements herein contained and other good and valuable consideration, the sufficiency and receipt of which are hereby acknowledged, and subject to the conditions set forth herein, the parties hereto hereby agree as follows:

SECTION 1. Defined Terms. As used in this Amendment, the following terms have the meanings specified below:

“Amendment Fee” shall have the meaning set forth in Section 8 hereof.

“Amendment Transactions” means the execution and delivery of this Amendment by each Person party hereto, the satisfaction of the conditions to the effectiveness hereof and the consummation of the transactions contemplated hereby, the MSSI Equity Contribution and the payment of a dividend to holders of Equity Interests in Holdings in an aggregate amount of up to $190,000,000.

“Amendment No. 4 Effective Date” shall mean the date on which this Amendment shall have become effective following the due satisfaction of the conditions set forth or referred to in Section 7(a) hereof.

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SECTION 2. Amendments to Section 1.01 of the Credit Agreement. (a) Section 1.01 of the Credit Agreement is hereby amended by adding the following definitions in the appropriate alphabetical order:

“Amendment No. 4” means Amendment No. 4 dated as of December 21, 2006, among Holdings, the Borrower, the Subsidiary Loan Parties party thereto, the Lenders party thereto and the Administrative Agent.

“Amendment No. 4 Effective Date” has the meaning set forth in Section 1 of Amendment No. 4.

“MSSI Equity Contribution” means the contribution by Morgan Stanley Strategic Investments, Inc. to Holdings of cash in an aggregate amount not to exceed $150,000,000 in exchange for shares of common stock of Holdings and shares of Qualified Preferred Stock of Holdings.

(b) The definition of the term “Permitted Security” in Section 1.01 of the Credit Agreement is hereby amended by (i) replacing the text “or” at the end of clause (a) with “,”, (ii) replacing the text “that makes an equity investment in Holdings in connection with the Transactions” beginning in the third line thereof with the text “holding any Equity Interest in Holdings as of the Amendment No. 4 Effective Date (after giving effect to the MSSI Equity Contribution) for cash” and (iii) inserting the text “or (c) Equity Interests issued to management, employees or consultants of Holdings, the Borrower or any of the Subsidiaries under any employment or similar agreement, stock option or stock purchase plan or benefit plan in existence from time to time” at the end thereof.

SECTION 3. Amendment to Section 6.08 of the Credit Agreement. Section 6.08 of the Credit Agreement is hereby amended by (i) deleting “and” at the end of clause (xiv), (ii) replacing the period at the end of cause (xv) with “; and” and (iii) inserting the following at the end thereof:

“(xvi) the Borrower may make Restricted Payments to Holdings (and Holdings may make Restricted Payments with such amounts) of (A) up to $150,000,000 solely with the proceeds of the MSSI Equity Contribution, (B) up to $40,000,000, provided that, in each case, at the time of such Restricted Payment, no Default shall have occurred and be continuing or would result therefrom and (C) up to $1,000,000 to pay any non-recurring fees, cash charges, costs and expenses incurred in connection with the MSSI Equity Contribution.”

SECTION 4. Amendment to Section 1.01 of the Collateral Agreement. The definition of the term “Obligations” in Section 1.01 of the Collateral Agreement is hereby amended by inserting the text “(other than Holdings)” immediately following the text “each Loan Party” in clause (b) thereof.

SECTION 5. Waivers. The undersigned Lenders hereby waive any Default arising under the Credit Agreement to the extent, but only to the extent, any such Default results from any guarantee of or any security granted under the Collateral Agreement prior to the Amendment No. 4 Effective Date for the due and punctual payment or performance in full of any Obligations (as defined in the Collateral Agreement prior to giving effect to Section 4 hereof) of Holdings under any Swap Agreement (it being understood that on and after the Amendment No. 4 Effective Date, the due and punctual payment and performance in full of all obligations of

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Holdings under any Swap Agreement shall not constitute “Obligations” under the Collateral Agreement as set forth in Section 4 hereof).

SECTION 6. Representations and Warranties. The Borrower and the undersigned Subsidiary Loan Parties jointly and severally represent and warrant to the Administrative Agent and to each of the Lenders that:

(a) This Amendment has been duly authorized, executed and delivered by Holdings, the Borrower and each Subsidiary Loan Party party hereto and constitutes a legal, valid and binding obligation of Holdings, the Borrower and each Subsidiary Loan Party party hereto enforceable against Holdings, the Borrower and each Subsidiary Loan Party party hereto in accordance with its terms, subject to applicable bankruptcy, insolvency, reorganization, moratorium or other laws affecting creditors’ rights generally and subject to general principles of equity, regardless of whether considered in a proceeding in equity or at law.

(b) The performance by any Loan Party of the Amendment Transactions (i) does not require any consent or approval of, registration or filing with, or any other action by, any Governmental Authority, except such as have been obtained or made and are in full force and effect, (ii) will not violate any Requirement of Law applicable to Holdings, the Borrower or any of the Subsidiaries, as applicable, (iii) will not violate or result in a default under any indenture, Management Services Agreement or other material agreement or instrument binding upon Holdings, the Borrower or any of the Subsidiaries or its assets, or give rise to a right thereunder to require any payment to be made by Holdings, the Borrower or any of the Subsidiaries or give rise to a right of, or result in, termination, cancelation or acceleration of any material obligation thereunder, (iv) will not result in a Limitation on any right, qualification, approval, permit, accreditation, authorization, Reimbursement Approval, license or franchise or authorization granted by any Governmental Authority, Third Party Payor or other Person applicable to the business, operations or assets of the Borrower or any of the Subsidiaries or adversely affect the ability of the Borrower or any of the Subsidiaries to participate in any Third Party Payor Arrangement except for Limitations, individually or in the aggregate, that are not material to the business of the Borrower and the Subsidiaries, taken as a whole, and (v) will not result in the creation or imposition of any Lien on any asset of Holdings, the Borrower or any of the Subsidiaries, except Liens created under the Loan Documents.

(c) The representations and warranties of each Loan Party set forth in the Loan Documents are true and correct in all material respects (except to the extent any such representation or warranty is qualified by “materially,” “Material Adverse Effect” or a similar term, in which case such representation and warranty shall be true and correct in all respects) on and as of the Amendment No. 4 Effective Date with the same effect as though made on and as of such date, except to the extent such representations and warranties expressly relate to an earlier date (in which case such representations and warranties were true and correct (or true and correct in all material respects, as the case may be) as of such earlier date).

(d) Immediately after giving effect to this Amendment, no Default shall have occurred and be continuing.

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SECTION 7. Conditions to Effectiveness; Amendments. (a) Sections 2, 3, 4 and 5 of this Amendment shall become effective as of the date first above written when (i) the Administrative Agent shall have received (A) in the case of Holdings and the Borrower, counterparts of this Amendment bearing the signatures of Holdings and the Borrower and (B) in the case of the Lenders, counterparts of this Amendment that, when taken together, bear the signatures of (x) the Required Lenders, (y) Tranche B Lenders holding Tranche B Term Loans representing more than 50% of the Tranche B Term Loans outstanding at such time and (z) Tranche C Lenders holding Tranche C Term Loans representing more than 50% of the Tranche C Term Loans outstanding at such time, (ii) the MSSI Equity Contribution shall have been consummated and (iii) all fees (including the Amendment Fee specified in Section 8 below) and, to the extent invoiced prior to the date hereof, expenses required to be paid or reimbursed by the Borrower under or in connection with this Amendment or the Credit Agreement shall have been paid or reimbursed, as applicable.

(b) This Amendment may not be amended nor may any provision hereof be waived except pursuant to a writing signed by Holdings, the Borrower, the Administrative Agent and the requisite Lenders under Section 9.02 of the Credit Agreement.

SECTION 8. Amendment Fee. In consideration of the agreements of the Lenders contained in this Amendment, the Borrower agrees to pay promptly to the Administrative Agent, for the account of each Lender that delivers an executed counterpart of this Amendment at or prior to 1:00 p.m., New York time, on December 15, 2006, an amendment fee (the “Amendment Fee”) in an amount equal to 0.025% of the sum of such Lender’s Revolving Exposure and outstanding Tranche B Term Loans and Tranche C Term Loans as of such time and date, provided that such Amendment Fee shall not be payable unless and until this Amendment becomes effective as provided in Section 7(a) above and upon such effectiveness such Amendment Fee shall be payable immediately.

SECTION 9. Credit Agreement and Collateral Agreement. Except as expressly set forth herein, this Amendment shall not by implication or otherwise limit, impair, constitute a waiver of, or otherwise affect the rights and remedies of the Lenders, the Agents, the Issuing Bank, Holdings, the Borrower or any other Loan Party under the Credit Agreement or any other Loan Document, and shall not alter, modify, amend or in any way affect any of the terms, conditions, obligations, covenants or agreements contained in the Credit Agreement or any other Loan Document, all of which are ratified and affirmed in all respects and shall continue in full force and effect. Nothing herein shall be deemed to entitle Holdings or the Borrower to any future consent to, or waiver, amendment, modification or other change of, any of the terms, conditions, obligations, covenants or agreements contained in the Credit Agreement or any other Loan Document in similar or different circumstances. After the Amendment No. 4 Effective Date, any reference to the Credit Agreement shall mean the Credit Agreement as modified hereby, provided that any reference in the Credit Agreement to the date of the Credit Agreement, as modified hereby, shall in all instances remain as of August 20, 2004, and references in the Credit Agreement to “the date hereof” and “the date of this Agreement,” and phrases of similar import, shall in all instances be and continue to refer to August 20, 2004, and not the date of this Amendment. After the Amendment No. 4 Effective Date, any reference to the Collateral Agreement shall mean the Collateral Agreement as modified hereby, provided that any reference in the Collateral Agreement to the date of the Collateral Agreement, as modified hereby, shall in

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all instances remain as of August 20, 2004, and references in the Collateral Agreement to “the date hereof” and “the date of this Agreement,” and phrases of similar import, shall in all instances be and continue to refer to August 20, 2004, and not the date of this Amendment

SECTION 10. Applicable Law; Waiver of Jury Trial. (A) THIS AMENDMENT SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAW OF THE STATE OF NEW YORK.

(B) EACH PARTY HERETO AGREES AS SET FORTH IN SECTION 9.10 OF THE CREDIT AGREEMENT AS IF SUCH SECTION WERE SET FORTH IN FULL HEREIN.

SECTION 11. Counterparts. This Amendment may be executed in counterparts (and by different parties hereto on different counterparts), each of which shall constitute an original, but all of which when taken together shall constitute a single contract. Delivery of an executed counterpart of a signature page of this Amendment by telecopy or other electronic transmission shall be as effective as delivery of a manually executed counterpart of this Amendment.

SECTION 12. Expenses. The Borrower agrees to reimburse the Administrative Agent, the Syndication Agent and the Documentation Agent for their reasonable out-of-pocket expenses in connection with this Amendment, including the reasonable fees, charges and disbursements of Cravath, Swaine & Moore LLP, counsel for the Administrative Agent.

SECTION 13. Headings. The Section headings used herein are for convenience of reference only, are not part of this Amendment and are not to affect the construction of, or to be taken into consideration in interpreting, this Amendment.

SECTION 14. Severability. Any provision of this Amendment held to be invalid, illegal or unenforceable in any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such invalidity, illegality or unenforceability without affecting the validity, legality and enforceability of the remaining provisions hereof; and the invalidity of a particular provision in a particular jurisdiction shall not invalidate such provision in any other jurisdiction. The parties shall endeavor in good-faith negotiations to replace the invalid, illegal or unenforceable provisions with valid provisions, the economic effect of which comes as close as possible to that of the invalid, illegal or unenforceable provisions.

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IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly executed by their respective authorized officers as of the day and year first written above.

US ONCOLOGY HOLDINGS, INC.,
By
	Name:
	Title:

US ONCOLOGY, INC.,
By
	Name:
	Title:

[SUBSIDIARY LOAN PARTIES],
By
	Name:
	Title:

JPMORGAN CHASE BANK, N.A., Individually and as Administrative Agent,
By
	Name:
	Title:

SIGNATURE PAGE TO AMENDMENT NO. 4 AMONG US ONCOLOGY HOLDINGS, INC., US ONCOLOGY, INC., THE SUBSIDIARY LOAN PARTIES PARTY THERETO, THE LENDERS PARTY THERETO AND JPMORGAN CHASE BANK, N.A., AS ADMINISTRATIVE AGENT.
Name of Institution:
by
	Name:
	Title:

EX-99.1

Exhibit 99.1

Contact:	Richard P. McCook
	Executive Vice President and
	Chief Financial Officer
	(832) 601-6274
	Rick.McCook@usoncology.com

US Oncology Holdings, Inc. Announces Completion of Equity Offering and

Declaration of Dividend to Stockholders

(Houston, December 22, 2006) US Oncology Holdings, Inc. (the “Company”) today announced the completion of the previously announced $150 million private offering of its common and preferred stock to Morgan Stanley Strategic Investments, Inc. As a result of the stock sale, Morgan Stanley Strategic Investments now owns approximately 14.7 percent of the common stock of the Company, on a fully diluted basis.

The net proceeds of the issuance of the stock, together with the cash-on-hand of US Oncology, Inc., the Company’s wholly owned operating subsidiary, will be used to pay a dividend of $190 million, or approximately $1.42 for each share of common or preferred stock, to the stockholders of the Company as of December 20, 2006. The dividend will be paid on January 3, 2007. Shares acquired by Morgan Stanley Strategic Investments were acquired after the record date and will not receive the dividend.

“We are very pleased with Morgan Stanley’s decision to invest in US Oncology. We believe Morgan Stanley brings a depth of experience in the financial markets as well as a vote of confidence in the valuation of our company,” said Dale Ross, chairman and CEO of US Oncology.

About US Oncology, Inc.

US Oncology, headquartered in Houston, is one of the nation’s largest cancer treatment and research networks. US Oncology provides extensive services and support to its affiliated cancer care sites nationwide to help them expand their offering of the most advanced treatments and technologies, build integrated community-based cancer care centers, improve their therapeutic drug management programs, and participate in many of the new cancer-related clinical research studies. US Oncology also provides a broad range of services to pharmaceutical manufacturers, including product distribution and informational services such as data reporting and analysis.

According to the company’s last quarterly earnings report, US Oncology is affiliated with 1,029 physicians operating in 411 locations, including 91 radiation oncology facilities in 35 states.

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