As filed with the Securities and Exchange Commission on June 9, 2010

Registration No. 333-110938

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 1 TO
REGISTRATION STATEMENT ON FORM S-3
UNDER THE SECURITIES ACT OF 1933

OSI PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

Delaware	13-3159796
(State or other jurisdiction of incorporation organization)	(I.R.S. Employer Identification No.)

420 Saw Mill River Road, Ardsley, New York 10502 (914) 231-8000

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Barbara A. Wood
Senior Vice President, General Counsel and Secretary
OSI Pharmaceuticals, Inc.
420 Saw Mill River Road, Ardsley, New York 10502 (914) 231-8000

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies of all communications to:

Katayun I. Jaffari, Esquire
Saul Ewing LLP
Centre Square West, 1500 Market Street, 38^th Floor, Philadelphia, Pennsylvania 19102-2186, (215) 972-7161

Approximate date of commencement of proposed sale to the public: Not applicable.

     If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box: o

     If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box: o

     If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

     If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

     If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. o

     If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. o

     Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer þ	Accelerated filer o	Non-accelerated filer o	Smaller reporting company o
		(Do not check if a smaller reporting company)

DEREGISTRATION OF SECURITIES

     This Post-Effective Amendment No. 1 relates to the Registration Statement on Form S-3 (Registration No. 333-110938), (the “Registration Statement”) of OSI Pharmaceuticals, Inc., a Delaware corporation (the “Company”), filed on December 5, 2003, as amended on February 13, 2004, pertaining to the registration of convertible notes and underlying shares of common stock of the Company.

     On June 8, 2010, pursuant to the terms of the Agreement and Plan of Merger, dated as of May 16, 2010, by and among the Company, Astellas Pharma Inc., Astellas US Holding, Inc. and Ruby Acquisition, Inc., Ruby Acquisition, Inc. merged with and into the Company (the “Merger,” and the date and time at which it became effective, the “Effective Time”), and the Company, as the surviving corporation in the Merger, became a wholly-owned subsidiary of Astellas US Holding, Inc. In connection with and as a result of the Merger, the Company has terminated all offerings of its securities pursuant to any existing registration statements. In accordance with an undertaking made by the Company in the Registration Statement, as amended, to remove from registration, by means of a post-effective amendment, any securities registered pursuant to the Registration Statement, as amended, that remain unsold at the termination of the offering, the Company hereby removes from registration all securities registered but unsold pursuant to the Registration Statement, as amended, as of the Effective Time.

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SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Post-Effective Amendment No. 1 to Registration Statement on Form S-3 to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Ardsley, State of New York, on this 9^th day of June, 2010.

OSI PHARMACEUTICALS, INC.
By:	/s/ Barbara A. Wood
	Barbara A. Wood
	Senior Vice President, General Counsel and Secretary

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