SC TO-T/A

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

________________

Amendment No. 15

to

SCHEDULE TO

(Rule 14d-100)

Tender Offer Statement under Section 14(d)(1) or 13(e)(1) of

the Securities Exchange Act of 1934

VENTANA MEDICAL SYSTEMS, INC.

(Name of Subject Company)

ROCKET ACQUISITION CORPORATION

ROCHE HOLDING LTD

(Names of Filing Persons — Offeror)

Common Stock, Par Value $0.001 Per Share

(including the associated preferred stock purchase rights)

(Title of Class of Securities)

________________

92276H106

(Cusip Number of Class of Securities)

Beat Kraehenmann

Roche Holding Ltd

Grenzacherstrasse 124

CH-4070 Basel

Switzerland

Telephone: +41-61-688-1111

(Name, Address and Telephone Number of Person Authorized to Receive Notices

and Communications on Behalf of Filing Persons)

Copies to:

Christopher Mayer

Davis Polk & Wardwell

450 Lexington Avenue

New York, New York 10017

Telephone: (212) 450-4000

CALCULATION OF FILING FEE

Transaction Valuation*	Amount of Filing Fee**
$2,978,902,500	$91,452.31

* Estimated for purposes of calculating the filing fee only. This amount assumes the purchase of all 33,668,000 shares of common stock of Ventana Medical Systems, Inc. outstanding as of March 31, 2007, all options outstanding as of March 31, 2007 with respect to 6,022,000 shares of common stock of Ventana, and all restricted stock and restricted stock units outstanding as of March 31, 2007 with respect to 28,700 shares of common stock of Ventana. The number of outstanding shares, options, and restricted stock and restricted stock units is contained in Ventana’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2007.

** The amount of the filing fee is calculated in accordance with Rule 0-11 of the Securities Exchange Act of 1934, as amended, by multiplying the transaction valuation by 0.0000307.

R Check box if any part of the fee is offset as provided by Rule 0-11(a)(2) and identify the filing with which the offsetting fee was previously paid. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

Amount Previously Paid:	$91,452.31	Filing Party:	Roche Holding Ltd
Form or Registration No.:	SC TO-T	Date Filed:	June 27, 2007

£ Check the box if the filing relates solely to preliminary communications made before the commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which the statement relates:

R third-party tender offer subject to Rule 14d-1.

£ issuer tender offer subject to Rule 13e-4.

£ going-private transaction subject to Rule 13e-3.

£ amendment to Schedule 13D under Rule 13d-2.

Check the following box if the filing is a final amendment reporting the results of the tender offer.  £

Items 1 through 5, Items 7 through 9 and Item 11.

This Amendment No. 15 to Tender Offer Statement on Schedule TO (the “Schedule TO”) amends and supplements the statement originally filed on June 27, 2007 by Roche Holding Ltd, a joint stock company organized under the laws of Switzerland (“Parent”), and Rocket Acquisition Corporation (the “Purchaser”), a Delaware corporation and an indirect wholly owned subsidiary of Parent. This Schedule TO relates to the offer by the Purchaser to purchase all outstanding shares of common stock, par value $0.001 per share (together with the associated preferred stock purchase rights, the “Shares”), of Ventana Medical Systems, Inc., a Delaware corporation (the “Company”), at $75.00 per Share, net to the seller in cash, without interest and less applicable withholding taxes, upon the terms and subject to the conditions set forth in the Offer to Purchase, dated June 27, 2007 (the “Offer to Purchase”), and in the related Letter of Transmittal (which, together with any amendments or supplements thereto, collectively constitute the “Offer”).

The information set forth in the Offer to Purchase, including all schedules thereto, and the related Letter of Transmittal is expressly incorporated herein by reference with respect to all of the items of this Schedule TO, except as otherwise set forth below.

All capitalized terms used in this Amendment No. 15 without definition have the meanings ascribed to them in the Schedule TO.

Item 6.  Purpose of the Transaction and Plans or Proposals.

On December 5, 2007, Roche announced that it had given notice to the Company, as required by the Company’s bylaws, that it will nominate independent candidates to replace the Company Board at the Company’s 2008 annual stockholders meeting.  Roche will nominate Dwight B. Crane, John J. Jones, Loring W. Knoblauch, and Michael L. Kranda for election to the Company’s four Class III director seats that are up for election at the Company’s 2008 annual stockholders meeting.  In addition, Roche intends to seek stockholder approval to amend the Company’s bylaws to eliminate the classified board and to remove all of the Company’s directors, other than the four Class III directors elected at the 2008 annual stockholders meeting.  If stockholders approve the elimination of the classified board and removal of directors, Roche intends to seek stockholder approval to amend the Company’s bylaws to reduce the size of the Company Board from 10 to seven members and to elect Bary G. Bailey, Jay B. Hunt and Anthony H. Wild to the three vacant seats on the Company Board.  If one or more of the individuals listed above is unable to serve on the Company Board, Roche intends to nominate Philip R. Lochner, Jr. and/or David A. Dodd as additional or substitute nominees.  The full text of a press release issued by Parent announcing that it had given notice to the Company is filed as Exhibit (a)(5)(xv) hereto and is incorporated herein by reference.

Item 10.  Financial Statements.

Not applicable.

Item 12.  Exhibits.

Item 12 is hereby amended and supplemented with the following information:

Exhibit (a)(5)(xv) Press Release issued by Roche Holding Ltd, dated December 5, 2007.

SIGNATURES

After due inquiry and to the best knowledge and belief of the undersigned, each of the undersigned certify that the information set forth in this statement is true, complete and correct.

Date: December 5, 2007

ROCKET ACQUISITION CORPORATION
By:	/s/ Beat Kraehenmann
	Name: Beat Kraehenmann
	Title:   Secretary
ROCHE HOLDING LTD
By:	/s/ Bruno Maier
	Name: Bruno Maier
	Title:   Authorized Signatory
By:	/s/ Beat Kraehenmann
	Name: Beat Kraehenmann
	Title:   Authorized Signatory

EXHIBIT INDEX

Exhibit No.	Description
(a)(1)(i)	Offer to Purchase dated June 27, 2007*
(a)(1)(ii)	Letter of Transmittal*
(a)(1)(iii)	Notice of Guaranteed Delivery*
(a)(1)(iv)	Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees*
(a)(1)(v)	Letter to Clients for use by Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees*
(a)(1)(vi)	Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9*
(a)(1)(vii)	Summary Advertisement dated June 27, 2007*
(a)(5)(i)	Press Release issued by Roche Holding Ltd, dated June 25, 2007*
(a)(5)(ii)	Complaint filed in the Court of Chancery of the State of Delaware in and for New Castle County on June 29, 2007*
(a)(5)(iii)	Complaint filed in the United States District Court for the District of Arizona on June 29, 2007*
(a)(5)(iv)	Press Release issued by Roche Holding Ltd, dated July 11, 2007*
(a)(5)(v)	Excerpt from an Investor Presentation by Roche Holding Ltd, dated July 19, 2007*
(a)(5)(vi)	Transcript of an Investor Presentation by Roche Holding Ltd, dated July 19, 2007*
(a)(5)(vii)	Press Release issued by Roche Holding Ltd, dated July 25, 2007*
(a)(5)(viii)	Press Release issued by Roche Holding Ltd, dated July 26, 2007*
(a)(5)(ix)	Press Release issued by Roche Holding Ltd, dated August 21, 2007*
(a)(5)(x)	Press Release issued by Roche Holding Ltd, dated August 22, 2007*
(a)(5)(xi)	Press Release issued by Roche Holding Ltd, dated September 19, 2007*
(a)(5)(xii)	Press Release issued by Roche Holding Ltd, dated October 29, 2007*
(a)(5)(xiii)	First Amended Complaint filed in the Court of Chancery of the State of Delaware in and for New Castle County on October 26, 2007*
(a)(5)(xiv)	Press Release issued by Roche Holding Ltd, dated November 13, 2007*
(a)(5)(xv)	Press Release issued by Roche Holding Ltd, dated December 5, 2007
(b)	Not applicable
(c)	Not applicable
(d)	Not applicable
(f)	Not applicable
(g)	Not applicable
(h)	Not applicable

________________

* Previously filed

EX-99.A.5.XV

Exhibit (a)(5)(xv)

Media Release

For Immediate Release

Basel, November 13, 2007

Roche To Nominate Independent Directors for Election at Ventana’s 2008 Annual Stockholders Meeting

Roche (SWX: ROG.VX; RO.S) announced today thatit gave notice to Ventana Medical Systems, Inc. (Nasdaq: VMSI), as required by Ventana’s bylaws, that it will nominate independent candidates to replace Ventana’s board of directors at Ventana’s 2008 annual stockholders meeting.

On June 27, 2007, Roche commenced a tender offer to acquire all of the outstanding common shares of Ventana for $75.00 per share in cash.  This price represents a 44% premium to Ventana’s close of $51.95 on June 22, 2007 (the last trading day prior to the announcement of Roche’s offer) and a 55% premium to its three-month average as of the same date of $48.30.  Recently, Roche entered into a confidentiality agreement with Ventana and has carried out limited due diligence.

Franz B. Humer, Chairman and CEO of Roche said, “We have taken this step, as required by Ventana’s bylaws, because we are committed to pursuing the acquisition of Ventana.  However, we continue to prefer a negotiated transaction.”

Dr. Humer continued, “All of our nominees have proven track records in their areas of expertise and, if elected, we are confident that they will act in the best interests of Ventana stockholders by exploring all alternatives for maximizing shareholder value.”

Nominees and Proposals

Roche intends to nominate the following candidates for election to Ventana’s four Class III director seats:

· Dwight B. Crane, Ph.D.  Dr. Crane was a professor at Harvard Business School from 1969 to June 2007 and is currently the George Fisher Baker, Jr. Professor of Business Administration, Emeritus, at Harvard Business School, the lead trustee of the Legg Mason Partners Equity Trust and the Legg Mason Partners Variable Equity Trust and a director of LMP Real Estate Income Fund, Inc. and Western Asset Municipal High Income Fund, Inc.

· John J. Jones.  Mr. Jones served as Senior Vice President and General Counsel of Argosy Gaming Company from January 2004 to October 2005, as Vice Chairman and General Counsel of Legal Advantage Services from December 2002 to January 2004, as Executive Vice President and General Counsel of RCN Corporation from July 1998 to December 2002 and is currently the Managing Director of J3 Capital and Executive Vice President of Imaging Advantage LLC.

· Loring W. Knoblauch.  Mr. Knoblauch served as President and Chief Executive Officer of Underwriters Laboratories, Inc. from April 2001 to December 2004, as President and Chief Executive Officer of Talon Automated Equipment Company from 1997 to 2001, as President of Honeywell Asia Pacific from 1986 to 1992 and is currently a member of the Operating Advisory Board of Prism Capital, Inc.

· Michael L. Kranda.  Mr. Kranda served as a Managing Director of Vulcan Venture Capital from September 2003 to December 2006, as Chief Executive Officer and President of Oxford GlycoSciences from July 1996 to July 2002 and is currently a consultant for Vulcan Venture Capital.

In addition, Roche intends to seek stockholder approval to amend Ventana’s bylaws to eliminate Ventana’s classified board and to remove all of the Ventana directors, other than the four Class III directors elected at the 2008 Annual Meeting.  If stockholders approve the elimination of the classified board and removal of directors, Roche intends to seek stockholder approval to amend Ventana’s bylaws to reduce the size of the Board of Directors from 10 to seven members and to elect the following candidates to the three vacant seats on the Board of Directors:

· Bary G. Bailey.  Mr. Bailey served as Executive Vice President and Chief Financial Officer of Valeant Pharmaceuticals International (formerly ICN Pharmaceuticals, Inc.) from December 2002 to May 2007 and as Executive Vice President, Strategy and Technology, of PacifiCare Health Systems, Inc. from July 2000 to December 2002.

· Jay B. Hunt.  Mr. Hunt has served as a Principal of The Development Group since 1993, served as Executive Vice President of FM Productions from 1988 to 1990, as Chief Executive Officer of FN Realty Services, Inc. from 1983 to 1987 and is currently the non-executive Chairman of DDi Corporation.

· Anthony H. Wild, Ph.D.  Dr. Wild has served as a general partner of Bows Pharmaceuticals AG since October 2006, served as the Chairman and Chief Executive Officer of MedPointe Pharmaceuticals, Inc. from September 2001 to April 2006, as President of the Warner-Lambert Company’s Global Pharmaceutical Sector from 1995 to 2000 and is currently a member of the Board of Directors of Millennium Pharmaceuticals, Inc.

In addition, Roche notified Ventana of its intent to nominate Philip R. Lochner, Jr. and/or David A. Dodd as additional or substitute nominees for election to Ventana’s Board of Directors if one or more of the nominees is unable to serve:

· Philip R. Lochner, Jr.  Mr. Lochner served as Senior Vice President and Chief Administrative Officer of Time Warner Inc. from 1991 to 1998, as a Commissioner of the Securities and Exchange Commission from March 1990 to July 1991 and is currently a member of the Board of Directors of Apria Healthcare Group Inc., Clarcor Inc., Crane Co., CMS Energy Corporation and Monster Worldwide Inc.

· David A. Dodd.  Mr. Dodd has served as Chairman, President and Chief Executive Officer of BioReliance Corporation since December 2007, served as Chief Executive Officer of Serologicals Corporation from June 2000 to July 2006, as Chief Executive Officer of Solvay Pharmaceuticals, Inc. from August 1995 to May 2000 and is currently the non-executive Chairman of Stem Cell Sciences plc.

Greenhill & Co. and Citi are acting as financial advisors to Roche and Davis Polk & Wardwell is acting as legal counsel.

About Roche

Headquartered in Basel, Switzerland, Roche is one of the world’s leading research-focused healthcare groups in the fields of pharmaceuticals and diagnostics. As the world’s biggest biotech company and an innovator of products and services for the early detection, prevention, diagnosis and treatmentof diseases, the Group contributes on a broad range of fronts to improving people’s health and quality of life. Roche is the world leader in in-vitro diagnostics and drugs for cancer and transplantation, a market leader in virology and active in other major therapeutic areas such as autoimmune diseases, inflammation, metabolic disorders and

diseases of the central nervous system. In 2006 sales by the Pharmaceuticals Division totaled 33.3 billion Swiss francs, and the Diagnostics Division posted sales of 8.7 billion Swiss francs. Roche has R&D agreements and strategic alliances with numerous partners, including majority ownership interests in Genentech and Chugai, and invests approximately 7 billion Swiss francs a year in R&D. Worldwide, the Group employs about 75,000 people.

Roche’s Diagnostics Division offers a uniquely broad product portfolio and supplies a wide array of innovative testing products and services to researchers, physicians, patients, hospitals and laboratories world-wide.

Roche commenced operations in the U.S. over 100 years ago and these operations include research and development centers that conduct leading-edge work in advancing disease detection and treatment. Our diagnostics and pharmaceuticals businesses in the U.S. employ more than 20,000 people and generate approximately $10 billion in sales (including Genentech), accounting for about 40% of the Roche Group's global annual revenues.

For further information, please visit www.roche.com.

All trademarks used or mentioned in this release are protected by law.

Further information

- All documents on the offer to Ventana’s shareholders: www.roche.com/info070625

Roche Group Media Office

Phone: +41 61 688 8888 / e-mail: basel.mediaoffice@roche.com

- Daniel Piller (Head of Roche Group Media Office)

- Baschi Dürr

Brunswick Group (for U.S. media)

Phone: +1 212 333 3810

- Steve Lipin

- Nina Devlin

MacKenzie Partners (for U.S. investors)

Phone: +1 212 929 5500

-Larry Dennedy

-Bob Marese

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

THIS DOCUMENT CONTAINS CERTAIN FORWARD-LOOKING STATEMENTS. THESE FORWARD-LOOKING STATEMENTS MAY BE IDENTIFIED BY WORDS SUCH AS ‘BELIEVES’, ‘EXPECTS’, ‘ANTICIPATES’, ‘PROJECTS’, ‘INTENDS’, ‘SHOULD’, ‘SEEKS’, ‘ESTIMATES’, ‘FUTURE’ OR SIMILAR EXPRESSIONS OR BY DISCUSSION OF, AMONG OTHER THINGS, STRATEGY, GOALS, PLANS OR INTENTIONS. VARIOUS FACTORS MAY CAUSE ACTUAL RESULTS TO DIFFER MATERIALLY IN THE FUTURE FROM

THOSE REFLECTED IN FORWARD-LOOKING STATEMENTS CONTAINED IN THIS DOCUMENT, AMONG OTHERS: (1) PRICING AND PRODUCT INITIATIVES OF COMPETITORS; (2) LEGISLATIVE AND REGULATORY DEVELOPMENTS AND ECONOMIC CONDITIONS; (3) DELAY OR INABILITY IN OBTAINING REGULATORY APPROVALS OR BRINGING PRODUCTS TO MARKET; (4) FLUCTUATIONS IN CURRENCY EXCHANGE RATES AND GENERAL FINANCIAL MARKET CONDITIONS; (5) UNCERTAINTIES IN THE DISCOVERY, DEVELOPMENT OR MARKETING OF NEW PRODUCTS OR NEW USES OF EXISTING PRODUCTS, INCLUDING WITHOUT LIMITATION NEGATIVE RESULTS OF CLINICAL TRIALS OR RESEARCH PROJECTS, UNEXPECTED SIDE-EFFECTS OF PIPELINE OR MARKETED PRODUCTS; (6) INCREASED GOVERNMENT PRICING PRESSURES; (7) INTERRUPTIONS IN PRODUCTION; (8) LOSS OF OR INABILITY TO OBTAIN ADEQUATE PROTECTION FOR INTELLECTUAL PROPERTY RIGHTS; (9) LITIGATION; (10) LOSS OF KEY EXECUTIVES OR OTHER EMPLOYEES; AND (11) ADVERSE PUBLICITY AND NEWS COVERAGE. THE STATEMENT REGARDING EARNINGS PER SHARE GROWTH IS NOT A PROFIT FORECAST AND SHOULD NOT BE INTERPRETED TO MEAN THAT ROCHE’S EARNINGS OR EARNINGS PER SHARE FOR ANY CURRENT OR FUTURE PERIOD WILL NECESSARILY MATCH OR EXCEED THE HISTORICAL PUBLISHED EARNINGS OR EARNINGS PER SHARE OF ROCHE.

ADDITIONAL INFORMATION AND WHERE TO FIND IT

THIS PRESS RELEASE IS FOR INFORMATIONAL PURPOSES ONLY AND DOES NOT CONSTITUTE AN OFFER TO PURCHASE OR A SOLICITATION OF AN OFFER TO SELL VENTANA’S COMMON STOCK. THE TENDER OFFER IS BEING MADE PURSUANT TO A TENDER OFFER STATEMENT ON SCHEDULE TO (INCLUDING THE OFFER TO PURCHASE, LETTER OF TRANSMITTAL AND OTHER RELATED TENDER OFFER MATERIALS) FILED BY ROCHE WITH THE SECURITIES AND EXCHANGE COMMISSION (SEC) ON JUNE 27, 2007. THESE MATERIALS, AS THEY MAY BE AMENDED FROM TIME TO TIME, CONTAIN IMPORTANT INFORMATION, INCLUDING THE TERMS AND CONDITIONS OF THE OFFER, THAT SHOULD BE READ CAREFULLY BEFORE ANY DECISION IS MADE WITH RESPECT TO THETENDER OFFER. INVESTORS AND STOCKHOLDERS CAN OBTAIN A FREE COPY OF THESE MATERIALS AND OTHER DOCUMENTS FILED BY ROCHE WITH THE SEC AT THE WEBSITE MAINTAINED BY THE SEC AT WWW.SEC.GOV. THE TENDER OFFER MATERIALS MAY ALSO BE OBTAINED

FOR FREE BY CONTACTING THE INFORMATION AGENT FOR THE TENDER OFFER, MACKENZIE PARTNERS AT (212) 929-5500 OR (800) 322-2885 (TOLL-FREE).

ROCHE WILL BE FILING A PROXY STATEMENT ON SCHEDULE 14A AND OTHER RELEVANT DOCUMENTS WITH THE SEC IN CONNECTION WITH ITS SOLICITATION OF PROXIES FOR THE 2008 ANNUAL MEETING (THE “PROXY STATEMENT”).  PROMPTLY AFTER FILING A DEFINITIVE PROXY STATEMENT WITH THE SEC, ROCHE WILL MAIL THE PROXY STATEMENT AND A PROXY CARD TO EACH VENTANA STOCKHOLDER ENTITLED TO VOTE AT THE 2008 ANNUAL MEETING.  INVESTORS AND STOCKHOLDERS ARE URGED TO READ THE PROXY STATEMENT CAREFULLY AND IN ITS ENTIRETY WHEN IT BECOMES AVAILABLE AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION.  INVESTORS AND STOCKHOLDERS WILL BE ABLE TO OBTAIN A FREE COPY OF THESE MATERIALS AT THE WEBSITE MAINTAINED BY THE SEC AT WWW.SEC.GOV.  IN ADDITION, DOCUMENTS FILED WITH THE SEC BY ROCHE MAY ALSO BE OBTAINED FOR FREE BY CONTACTING MACKENZIE PARTNERS AT (212) 929-5500 OR (800) 322-2885 (TOLL-FREE).

ROCHE HOLDING LTD, ROCHE HOLDINGS, INC., ROCKET ACQUISITION CORPORATION AND THE INDIVIDUALS NOMINATED BY ROCHE HOLDINGS, INC. FOR ELECTION TO VENTANA’S BOARD OF DIRECTORS (THE “ROCHE NOMINEES”) MAY BE DEEMED TO BE PARTICIPANTS IN THE SOLICITATION OF PROXIES FROM VENTANA STOCKHOLDERS FOR USE AT THE 2008 ANNUAL MEETING OF STOCKHOLDERS, OR AT ANY ADJOURNMENT OR POSTPONEMENT THEREOF.  THE DIRECTORS AND EXECUTIVE OFFICERS OF ROCHE HOLDING LTD, ROCHE HOLDINGS, INC. AND ROCKET ACQUISITION CORPORATION WHO MAY BE PARTICIPANTS IN THE SOLICITATION OF PROXIES HAVE NOT BEEN DETERMINED AS OF THE DATE OF THIS PRESS RELEASE.  NO ADDITIONAL COMPENSATION WILL BE PAID TO SUCH DIRECTORS AND EXECUTIVE OFFICERS FOR SUCH SERVICES.  IN THEIR ROLE AS FINANCIAL ADVISORS TO ROCHE, GREENHILL & CO. AND CITI MAY ALSO ASSIST IN THE SOLICITATION OF PROXIES FROM VENTANA STOCKHOLDERS.  GREENHILL & CO. AND CITI WILL NOT RECEIVE ANY FEES FOR OR IN CONNECTION WITH ITS SOLICITATION ACTIVITIES, OTHER THAN THE FEES DUE FOR THEIR SERVICES AS FINANCIAL ADVISORS TO ROCHE AND DEALER MANAGERS IN CONNECTION WITH ROCHE’S TENDER OFFER.  INVESTORS AND STOCKHOLDERS

CAN OBTAIN ADDITIONAL INFORMATION REGARDING THE DIRECT AND INDIRECT INTERESTS OF THE ROCHE NOMINEES AND OTHER PARTICIPANTS BY READING THE DEFINITIVE PROXY STATEMENT WHEN IT BECOMES AVAILABLE.