Filed by: OSI Pharmaceuticals, Inc.
      Pursuant to Rule 425 under the Securities Exchange Act of 1933, as amended
                                            Subject Company: Cell Pathways, Inc.
                                                   Commission File No.: 00024889
                             Agreement and Plan of Merger filed as an exhibit to
                                             Form 8-K filed on February 11, 2003

   This filing relates to the proposed merger (the "Merger") whereby OSI
 Pharmaceuticals, Inc ("OSI") has agreed to acquire Cell Pathways, Inc. ("Cell
 Pathways") pursuant to the terms of an Agreement and Plan of Merger, dated as
 of February 7, 2003 (the "Merger Agreement"), by and among OSI, CP Merger
 Corporation and Cell Pathways.

   The Merger Agreement is on file with the Securities and Exchange Commission
as an exhibit to the Current Report on Form 8-K filed by OSI today, February 11,
2003, and is incorporated by reference into this filing.

INFORMATION ABOUT THE MERGER AND WHERE TO FIND IT

   In connection with the proposed Merger, OSI will file with the SEC a
 registration statement on Form S-4. The registration statement will include a
 proxy statement of Cell Pathways for a meeting of its stockholders to consider
 and vote upon the proposed merger. The registration statement will also serve
 as a prospectus of OSI with respect to the shares of OSI to be distributed to
 stockholders of Cell Pathways in the proposed transaction. OSI and Cell
 Pathways will file the proxy statement/prospectus with the SEC as soon as
 practicable.  INVESTORS AND SECURITY HOLDERS ARE URGED TO CAREFULLY READ THE
 PROXY STATEMENT/PROSPECTUS REGARDING THE PROPOSED MERGER TRANSACTION, WHEN IT
 BECOMES AVAILABLE, AND ANY OTHER DOCUMENTS FILED WITH THE SEC, BECAUSE THEY
 WILL CONTAIN IMPORTANT INFORMATION ABOUT OSI, CELL PATHWAYS, THE MERGER AND
 RELATED MATTERS.

    Investors and security holders will be able to obtain a free copy of the
 proxy statement/prospectus (when it is available) and other documents filed by
 OSI at the SEC's web site at http://www.sec.gov. In addition, you may obtain
 documents filed with the SEC by OSI free of charge by requesting them in
 writing from OSI Pharmaceuticals, Inc., 58 South Service Road, Suite 110,
 Melville, New York 11747, Attention: Investor Relations, telephone: (631)
 962-2000.