SC TO-T/A

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE TO

(Rule 14d-100)

TENDER OFFER STATEMENT UNDER SECTION 14(d)(1)

OR 13(e)(1) OF THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 10)

OSI Pharmaceuticals, Inc.

(Name of Subject Company (Issuer))

Ruby Acquisition, Inc.

Astellas US Holding, Inc.

Astellas Pharma Inc.

(Name of Filing Persons (Offerors))

Common Stock, Par Value $.01 Per Share

(Including the Associated Stock Purchase Rights)

(Title of Class of Securities)

671040103

(CUSIP Number of Class of Securities)

Masafumi Nogimori

President and Chief Executive Officer

Astellas Pharma Inc.

3-11, Nihonbashi-Honcho

2-chome, Chuo-ku

Tokyo 103-8411, Japan

(81) 3-3244-3000

(Name, Address and Telephone Number of Person Authorized

to Receive Notices and Communications on Behalf of Filing Persons)

Copies to:

Michael O. Braun, Esq.

Craigh Leonard, Esq.

Morrison & Foerster LLP

1290 Avenue of the Americas

New York, New York 10104

(212) 468-8000

CALCULATION OF FILING FEE

Transaction Valuation*	Amount of Filing Fee**
$4,241,680,815	$302,432

* For purposes of calculating the amount of filing fee only in accordance with Rules 0-11(d) and 0-11(a)(4) under the Securities Exchange Act of 1934 (the “Exchange Act”). Based on the offer to purchase up to 73,768,362 shares of common stock, par value $0.01 per share of OSI Pharmaceuticals, Inc. (the “Company”), including the associated stock purchase rights, at a purchase price of $57.50 per share net to the seller in cash, without interest and subject to any required withholding of taxes. Such number of shares consists of (i) 61,201,595 shares of common stock issued and outstanding as of April 30, 2010, as represented in the merger agreement dated May 16, 2010 between the Company and the filing persons (the “Merger Agreement”), minus the 1,000 shares of common stock beneficially owned by the filing persons as of the date hereof, (ii) all options outstanding as of April 30, 2010 with respect to 5,681,575 shares of the Company’s common stock, as represented in the Merger Agreement, (iii) 3,920,201 shares of common stock issuable on the conversion of the $115,000,000 outstanding face amount of the Company’s 2% Convertible Senior Subordinated Notes due 2025, as represented in the Merger Agreement, and (iv) 2,965,991 shares of common stock issuable on the conversion of the $160,000,000 outstanding face amount of the Company’s 3% Convertible Senior Subordinated Notes due 2038, as represented in the Merger Agreement.

** The filing fee was calculated in accordance with Rule 0-11 under the Exchange Act, as amended, by multiplying the transaction value by .00007130.

x Check the 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: $270,211	Filing Party: Ruby Acquisition, Inc. Astellas US Holding, Inc. Astellas Pharma Inc.
Form or Registration No.: SC TO	Date Filed: March 2, 2010
Amount Previously Paid: $32,221	Filing Party: Ruby Acquisition, Inc. Astellas US Holding, Inc. Astellas Pharma Inc.
Form or Registration No.: SC TO-T/A	Date Filed: May 17, 2010

¨ 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:

x 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:  ¨

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This Amendment No. 10 to Schedule TO (this “Amendment No. 10”) amends and supplements the Tender Offer Statement on Schedule TO as originally filed with the Securities and Exchange Commission on March, 2, 2010 (together with any amendments and supplements thereto the “Schedule TO”) relating to the offer by Ruby Acquisition, Inc. (“Purchaser”), a wholly-owned subsidiary of Astellas US Holding, Inc. (“Parent”), a wholly-owned subsidiary of Astellas Pharma Inc. (“Astellas”), to purchase all issued and outstanding shares of the common stock, par value $0.01 per share (the “Common Stock”, and together with the associated stock purchase rights, the “Shares”), of OSI Pharmaceuticals, Inc., a Delaware corporation (the “Company”), at a price of $57.50 per Share, net to the seller in cash, without interest and subject to any required withholding of taxes, upon the terms and subject to the conditions set forth in the Offer to Purchase dated March 2, 2010 (together with any amendments and supplements thereto the “Offer to Purchase”) and in the related Letter of Transmittal, as amended or supplemented from time to time. This Amendment No. 10 is being filed on behalf of Astellas, Parent and Purchaser. You should read this Amendment No. 10 together with the Schedule TO. All capitalized terms used in this Amendment No. 10 and not otherwise defined have the respective meanings ascribed to them in the Offer to Purchase.

The information set forth in the Offer to Purchase, including Schedule I thereto, is hereby incorporated by reference in answer to Items 1 through 13 of this Schedule TO, and is supplemented by the information specifically provided herein.

Item 12. Exhibits

Item 12 of the Schedule TO is hereby amended and supplemented to add the following exhibits:

(a)(5)(O)	Astellas Pharma Inc. Letter to OSI Pharmaceuticals, Inc. Employees dated May 16, 2010
(a)(5)(P)	Transcript of video presentation made by Masafumi Nogimori, Chief Executive Officer of Astellas Pharma Inc., to employees of OSI Pharmaceuticals on May 16, 2010.

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SIGNATURES

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

Dated May 17, 2010

ASTELLAS PHARMA INC.		ASTELLAS US HOLDING, INC.
By:	/s/    LINDA FRIEDMAN	By:	/s/    SEIGO KASHII
Name:	Linda Friedman as attorney-in-fact	Name:	Seigo Kashii
		Title:	Director, President & CEO
		RUBY ACQUISITION, INC.
		By:	/s/    Seigo Kashii
		Name:	Seigo Kashii
		Title:	Director, President & CEO

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints each of Seigo Kashii, Linda F. Friedman and Stephen Knowles, individually and severally, and with full power of substitution, the undersigned’s true and lawful attorney-in-fact with full power to execute and file with the Securities and Exchange Commission and any stock exchange or similar authority, any report required to be filed pursuant to Section 14 of the Securities Exchange Act of 1934, (as amended, the “Act”), with respect to a third-party tender offer subject to Rule 14d-1, giving and granting unto said attorney-in-fact the power and authority to act in the premises as fully and to all intents and purposes as the Company might or could do if personally present by one of its authorized signatories, hereby ratifying and confirming all that said attorney-in-fact shall lawfully do or cause to be done by virtue hereof.

This Power of Attorney shall remain in full force and effect until the earliest of: (i) a revocation in writing by the undersigned; (ii) such time as the person to whom power of attorney has been hereby granted ceases to be an employee of the undersigned or any subsidiary company thereof; or (iii) March 2, 2011.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of this 2nd day of March, 2010.

ASTELLAS PHARMA INC.
By:	/s/    MASAFUMI NOGIMORI
Name:	Masafumi Nogimori
Title:	Director, President & CEO

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EXHIBIT INDEX

Exhibit No.	Description
(a)(1)(A)	Offer to Purchase dated March 2, 2010.*
(a)(1)(B)	Form of Letter of Transmittal.*
(a)(1)(C)	Form of Notice of Guaranteed Delivery.*
(a)(1)(D)	Form of Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.*
(a)(1)(E)	Form of Letter to Clients for Use by Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.*
(a)(1)(F)	Guidelines for Certification of Taxpayer Identification Number on Substitute W-9.*
(a)(1)(G)	Summary Advertisement as published on March 2, 2010.*
(a)(5)(A)	Press Release issued by Astellas on March 1, 2010 incorporated herein by reference to the Schedule TO filed by Astellas on March 1, 2010.*
(a)(5)(B)	Press Release issued by Astellas dated March 2, 2010 regarding the commencement of the Offer and the lawsuit filed by Astellas US Holding, Inc. against OSI Pharmaceuticals, Inc.*
(a)(5)(C)	Complaint filed in Delaware Chancery Court against OSI Pharmaceuticals, Inc. and its directors.*
(a)(5)(D)	Letter regarding the Tender offer was distributed to certain public officials by Astellas.*
(a)(5)(E)	Press Release issued by Astellas dated March 15, 2010 regarding Astellas’ response to OSI Pharmaceuticals’ Rejection of its Offer.*
(a)(5)(F)	Press Release issued by Astellas dated March 16, 2010 regarding Astellas’ announcement of a full slate of independent director nominees for election at OSI Pharmaceuticals, Inc.’s 2010 Annual Stockholders Meeting.*
(a)(5)(G)	Press Release issued by Astellas dated March 19, 2010 regarding Astellas’ announcement of the expiration of the HSR waiting period for the Offer.*
(a)(5)(H)	Press Release issued by Astellas dated March 19, 2010 regarding Astellas’ announcement of changes to its director nominees for election to OSI Pharmaceuticals, Inc.’s Board of Directors.*
(a)(5)(I)	Press Release issued by Astellas dated March 29, 2010 regarding Astellas’ announcement of the execution of a confidentiality agreement with OSI Pharmaceuticals, Inc.*
(a)(5)(J)	Press Release issued by Astellas dated March 31, 2010 regarding Astellas’ announcement of the extension of the Offer.*
(a)(5)(K)	Presentation regarding Astellas’ offer to acquire OSI Pharmaceuticals dated April 2010.*
(a)(5)(L)	Press Release issued by Astellas dated April 23, 2010 regarding Astellas’ announcement of the extension of the Offer.*
(a)(5)(M)	Press Release issued by Astellas and OSI Pharmaceuticals dated May 16, 2010 announcing the execution of a Merger Agreement.*
(a)(5)(N)	Press Release issued by Astellas dated May 17, 2010 announcing the extension of the Offer.*

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(a)(5)(O)	Astellas Pharma Inc. Letter to OSI Pharmaceuticals, Inc. Employees dated May 16, 2010.
(a)(5)(P)	Transcript of video presentation made by Masafumi Nogimori, Chief Executive Officer of Astellas Pharma Inc., to employees of OSI Pharmaceuticals on May 16, 2010.
(b)	Not applicable.
(d)(1)	Agreement and Plan of Merger, by and among Astellas Pharma Inc., Astellas US Holding, Inc., Ruby Acquisition, Inc. and OSI Pharmaceuticals, Inc., dated May 17, 2010*
(g)	Not applicable.
(h)	Not applicable.

* Previously filed with Schedule TO.

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EX-99.(A)(5)(O)

Exhibit (a)(5)(o)

May 16, 2010

Dear OSI Employee,

I am writing to tell you how excited I am about today’s announcement that Astellas Pharma Inc. and OSI Pharmaceuticals, Inc. have reached an agreement to combine the two companies and work together on a shared mission to provide innovative new medicines to patients around the world.

OSI is a company with outstanding talent in oncology and diabetes that Astellas will be honored to work with towards a shared goal of improving the health of people around the world through the provision of innovative and reliable pharmaceutical products. We have great respect for you and the company you are part of and we expect to integrate the strengths of OSI into Astellas’ operations, as we have done on previous occasions.

This merger is about the combined growth that will come from a broader portfolio of products. Adding Astellas’ strong organization and experience in the development and sales of new products to the high quality research and development capabilities of both companies will enable the combined company to develop more products and bring them to market with greater speed and efficiency.

Thanks to your knowledge and expertise, OSI is a great strategic fit for Astellas. The combination with OSI provides Astellas with an expanded product portfolio in addition to a top-tier oncology platform in the U.S., a high priority therapeutic area for us. Today’s agreement supports Astellas’ stated growth strategy of becoming a Global Category Leader in oncology.

Your management team will keep you informed with any relevant updates, and I hope to have the opportunity to talk with many of you in person in the near future. I also hope to be able to share with you our plans for the integration of OSI into the Astellas Global Group very soon. In the meantime, to learn more about Astellas, who we are and what we do, please visit www.astellas.com or visit our YouTube channel at www.youtube.com/astellasus, where you can view our latest corporate video. Please also see the attached advertorial from the Financial Times that provides some background on Astellas.

I have also recorded a video message that has been posted on your internal portal today.

I sincerely look forward to welcoming you to Astellas group and working with you to achieve the vision we have set forth.

Yours sincerely,

Masafumi Nogimori

President and Chief Executive Officer

Astellas Pharma Inc.

Important additional information

This letter is for informational purposes only and does not constitute an offer to purchase or a solicitation of an offer to sell OSI’s common stock. The tender offer (“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) initially filed by Astellas Pharma Inc.

(“Astellas”) with the Securities and Exchange Commission (the “SEC”) on March 2, 2010. 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 the Tender Offer. Investors and shareholders can obtain a free copy of these materials and other documents filed by Astellas 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, Georgeson Inc. at (212) 440-9800.

OSI Pharmaceuticals’ (“OSI”) stockholders should read the company’s solicitation/recommendation statement on schedule 14D-9, which was initially filed with the SEC on March 15, 2010, and any amendments or supplements thereto. The company’s solicitation/recommendation statement will set forth the reasons for the recommendation of the OSI’s board and related information. The solicitation/recommendation statement and other public filings made from time to time by OSI with the SEC are available without charge from the SEC’s website at www.sec.gov, at OSI’s website at www.osip.com or from OSI’s information agent, by calling 800-322-2885 toll free or (212) 929-5500 or by emailing osipharma@mackenziepartners.com.

Statement of Cautionary Factors

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 growth is not a profit forecast and should not be interpreted to mean that Astellas’ 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 Astellas.

EX-99.(A)(5)(P)

Exhibit (a)(5)(p)

Video script for message from Masafumi Nogimori, President and Chief Executive Officer, Astellas Pharma Inc. to OSIP Employees

Script:

Hello everyone. My name is Masafumi Nogimori, and as the President and CEO of Astellas Pharma I am delighted that we have reached an agreement with the board of OSI Pharmaceuticals to bring our companies together.

Despite the activity and media coverage of the last few months, I presume that many of you are not very familiar with Astellas and would like to learn more. You no doubt have questions about the merger agreement, your role as part of Astellas, and what this is all going to mean for you.

The actual process of completing the transaction still has to run its course, so at the moment there are many details I simply cannot provide. We will update you on those developments when it is appropriate to do so. Today, I wanted to take the opportunity to emphasize two important points to help you understand our fundamental approach with regard to OSI.

The first is that our goal in integrating our businesses is growth through maximizing the potential of assets of both companies. It is not about squeezing out cost savings. We firmly believe that by bringing our businesses together we can make them much greater than the sum of their parts. Together, we can develop more high-quality therapies and bring them to market with greater speed and efficiency. OSI is an excellent company that we at Astellas will be honored to work with toward a shared goal of improving the health of people around the world.

The second point is that this merger agreement covers OSI as a whole. I strongly believe that there is a compelling strategic fit between the companies, and that’s why we have worked so hard to create this transaction.

We are fully aware that in any business integration like this, there is a lot of care and attention needed to bring two corporate cultures together. Astellas itself was created through a merger of two Japanese pharmaceutical companies, Fujisawa and Yamanouchi, in 2005. Since then, we have successfully conducted strategic alliances and acquisitions globally, and implemented business integration in other cases, such as the acquisition of Agensys, in the United States. We have learned a lot from these experiences and firmly believe that we can successfully combine our two businesses based on mutual understanding and respect. Today’s pharmaceutical business is totally globalized and healthcare is a universal concern, and as we learn more about each other, I hope you will see for yourself our commitment to cross-border understanding and mutual respect in everything we do.

In closing, I want to say again that the purpose of this deal is to create a strong, growth-oriented business that can truly hold its own in the global arena. Joining together is going to create exciting new opportunities for all our talented people. I speak for everyone at Astellas when I say we are committed to using our combined expertise to turn those opportunities into a great business that we can all be proud of. I very much look forward to working with you toward our shared goals.

Important additional information

This video script is for informational purposes only and does not constitute an offer to purchase or a solicitation of an offer to sell OSI’s common stock. The tender offer (“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) initially filed by Astellas Pharma Inc. (“Astellas”) with the Securities and Exchange Commission (the “SEC”) on March 2, 2010. 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 the Tender Offer. Investors and shareholders can obtain a free copy of these materials and other documents filed by Astellas 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, Georgeson Inc. at (212) 440-9800.

OSI Pharmaceuticals’ (“OSI”) stockholders should read the company’s solicitation/recommendation statement on schedule 14D-9, which was initially filed with the SEC on March 15, 2010, and any amendments or supplements thereto. The company’s solicitation/recommendation statement will set forth the reasons for the recommendation of the OSI’s board and related information. The solicitation/recommendation statement and other public filings made from time to time by OSI with the SEC are available without charge from the SEC’s website at www.sec.gov, at OSI’s website at www.osip.com or from OSI’s information agent, by calling 800-322-2885 toll free or (212) 929-5500 or by emailing osipharma@mackenziepartners.com.

Statement of Cautionary Factors

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 growth is not a profit forecast and should not be interpreted to mean that Astellas’ 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 Astellas.