<PAGE>


                                                                    EXHIBIT 10.1



        Portions of this Exhibit have been redacted and are the subject of a
confidential treatment request filed with the Secretary of the Securities and
Exchange Commission.



<PAGE>

                                                                    EXHIBIT 10.1








                             CO-PROMOTION AGREEMENT


                                     between



                            OSI PHARMACEUTICALS, INC.



                                       and



                                ARES TRADING S.A.



                           dated as of March 11, 2003



<PAGE>


                                Table of Contents
<TABLE>
<CAPTION>
                                                                                           Page
                                                                                           ----
<S>         <C>                                         `                                  <C>
ARTICLE I        DEFINITIONS.................................................................1

ARTICLE II       OSI'S RIGHTS AND RESPONSIBILITIES..........................................11
     2.1.   Grant of Rights.................................................................11
     2.2.   Oncology Marketing..............................................................11
     2.3.   Compliance......................................................................12
     2.4.   Sales Representatives...........................................................13
     2.5.   Marketing Management Team.......................................................14
     2.6.   Medical Science Liaisons........................................................14
     2.7.   Training........................................................................14
     2.8.   National Launch Meeting and Periodic Sales Meetings.............................16
     2.9.   Detailing.......................................................................16
     2.10.  Promotional Materials...........................................................16
     2.11.  Samples.........................................................................17
     2.12.  Clinical Trials.................................................................19
     2.13.  Promotional Activities..........................................................21
     2.14.  MSL Activities..................................................................21
     2.15.  Activities Reports..............................................................22
     2.16.  Communication...................................................................22

ARTICLE III      MANAGEMENT OF CO-PROMOTION.................................................22
     3.1.   Joint Management Committee......................................................22
     3.2.   Meetings........................................................................23
     3.3.   Decision Making.................................................................23
     3.4.   Responsibilities................................................................23
     3.5.   Retention of Rights.............................................................25

ARTICLE IV       REGULATORY MATTERS.........................................................25
     4.1.   Regulatory Approvals............................................................25
     4.2.   Communications with the FDA.....................................................25
     4.3.   Submissions to the FDA..........................................................26
     4.4.   Investigations..................................................................26
     4.5.   Recalls.........................................................................26
     4.6.   OSI Notification................................................................26
     4.7.   Adverse Drug Experiences and Technical Complaints...............................27
     4.8.   Inquiries.......................................................................27

ARTICLE V        SERONO'S RIGHTS AND RESPONSIBILITIES.......................................28
     5.1.   Product Pricing and Discounting.................................................28
     5.2.   Contracting with Organizations..................................................28
     5.3.   Approval of Promotional Materials, Training Materials and Materials used in
            the Conduct of MSL Activities...................................................28
     5.4.   Distribution and Sales..........................................................29
</TABLE>



<PAGE>

<TABLE>
<S>         <C>                                                                           <C>
     5.5.   Compliance with Codes and Standards.............................................29
     5.6.   Communication...................................................................29
     5.7.   Manufacturing Rights/Obligations................................................29
     5.8.   NDA/Regulatory..................................................................30
     5.9.   Product Supply..................................................................30
     5.10.  Inventory.......................................................................30
     5.11.  Compliance......................................................................30
     5.12.    **............................................................................30
     5.13.  MS Marketing Plan...............................................................30
     5.14.  Availability of Data............................................................31
     5.15.  Website.........................................................................31
     5.16.    ** ...........................................................................32
     5.17.  Indigent Patient Program........................................................32
     5.18.  Sales Report....................................................................32
     5.19.  IMS Data........................................................................32

ARTICLE VI       PAYMENT....................................................................32
     6.1.   Initial Fee.....................................................................32
     6.2.   Transition Services Fee.........................................................33
     6.3.   Maintenance Fee.................................................................33
     6.4.   Net Sales Report................................................................33
     6.5.   Net Sales Determination.........................................................33
     6.6.   Commission Payment..............................................................34
     6.7.   Payment Currency................................................................35
     6.8.   Payments........................................................................35
     6.9.   Taxes...........................................................................36
     6.10.  Withholding Taxes...............................................................36

ARTICLE VII      ACCOUNTING AND REPORTS.....................................................36
     7.1.   Books and Records...............................................................36
     7.2.   Audit...........................................................................37
     7.3.   Sales Force Efforts.............................................................38

ARTICLE VIII     INTELLECTUAL PROPERTY RIGHTS...............................................38
     8.1.   Trademark and Corporate Logos...................................................38
     8.2.   Copyrights......................................................................39
     8.3.   Know-How........................................................................40
     8.4.   Patent..........................................................................40
     8.5.   License Agreement and Manufacturing Agreement...................................41

ARTICLE IX       CONFIDENTIAL INFORMATION...................................................41
     9.1.   Treatment of Confidential Information...........................................41
     9.2.   Disclosure to Affiliates and Agents.............................................41
     9.3.   Injunctive Relief...............................................................42
</TABLE>


----------
** This portion has been redacted pursuant to a confidential treatment request.

<PAGE>

<TABLE>
<S>         <C>                                                                            <C>
ARTICLE X        REPRESENTATIONS, WARRANTIES AND INDEMNIFICATION............................42
     10.1.  Serono's Representations........................................................42
     10.2.  OSI's Representations...........................................................44
     10.3.  Indemnification of OSI..........................................................45
     10.4.  Indemnification of Serono.......................................................45
     10.5.  Indemnification Procedures for Third Party Claims...............................46
     10.6.  Non-Duplicative Payment.........................................................47
     10.7.  Insurance.......................................................................47
     10.8.  Limitation of Liability.........................................................47

ARTICLE XI       TERM AND TERMINATION.......................................................48
     11.1.  Term............................................................................48
     11.2.  Termination for Breach..........................................................48
     11.3.  Termination Upon Other Events...................................................48
     11.4.  Termination after the First Generic Date........................................48
     11.5.  Termination for Bankruptcy......................................................48
     11.6.  Survival of Obligations.........................................................49

ARTICLE XII Non-Competition.................................................................50
     12.1.  **..............................................................................50
     12.2.  **..............................................................................50

ARTICLE XIII     DISPUTE RESOLUTION.........................................................50
     13.1.  Disputes Concerning Matters Subject to Determination by the JMC.................50
     13.2.  Other Disputes..................................................................51

ARTICLE XIV      MISCELLANEOUS..............................................................51
     14.1.  Entire Agreement................................................................51
     14.2.  Governing Law...................................................................51
     14.3.  Notices.........................................................................52
     14.4.  Force Majeure...................................................................53
     14.5.  Assignment......................................................................54
     14.6.  Performance by an Affiliate.....................................................54
     14.7.  Amendments and Waivers..........................................................54
     14.8.  Severability....................................................................55
     14.9.  Counterparts....................................................................55
     14.10. Relationship of the Parties.....................................................55
     14.11. Non-Solicitation of Employees...................................................55
     14.12. Press Releases..................................................................56
     14.13. Third Party Beneficiaries.......................................................56
     14.14. Headings........................................................................57
     14.15. Interpretation..................................................................57
     14.16. Further Assurances; Covenant to Cooperate.......................................57
</TABLE>

----------
** This portion has been redacted pursuant to a confidential treatment request.

<PAGE>

<TABLE>
     <S>                                                                                   <C>
14.17. No Set Off......................................................................57
</TABLE>



<PAGE>

                             CO-PROMOTION AGREEMENT

        THIS CO-PROMOTION AGREEMENT (the "Agreement"), dated as of March 11,
2003 (the "Effective Date"), between ARES TRADING S.A. ("Serono"), a corporation
organized under the laws of Switzerland and having a principal place of business
at Chateau de Vaumarcus, 2028 Vaumarcus, Switzerland, and OSI PHARMACEUTICALS,
INC. ("OSI"), a corporation organized under the laws of Delaware and having
executive offices at 58 South Service Road, Suite 110, Melville, New York 11747;

                                   WITNESSETH:

        WHEREAS, Serono and OSI would like to set forth the terms and conditions
pursuant to which they will collaborate in connection with the promotion and
marketing of the Product in the Field in the Territory (as such terms are
defined below);

        NOW, THEREFORE, based on the premises and the mutual covenants and
obligations set forth below, and intending to be bound hereby, the parties agree
as follows:

                                    ARTICLE I

                                   DEFINITIONS

        The following terms, whether used in the singular or plural, shall have
the following meanings:

        1.1. "Act" means the United States Food, Drug and Cosmetic Act, as
amended from time to time, and the regulations promulgated thereunder including
the guidelines and guidance issued by the FDA.

        1.2. "Activities Report" means the report described in Section 2.15.

<PAGE>

        1.3. "Affiliate" means any entity that directly or indirectly controls,
is controlled by, or is under common control with, a party to this Agreement,
but only for so long as such control shall continue. For purposes of this
definition, "control" (including, with correlative meanings, "controlled by,"
"controlling" and "under common control with") means possession, directly or
indirectly, of (i) the power to direct or cause the direction of the management
and policies of an entity (whether through ownership of securities or
partnership or other ownership interests, by contract or otherwise), or (ii) at
least fifty percent (50%) of the voting securities or other comparable equity
interests.

        1.4. "Breaching Party" shall have the meaning set forth in Section 11.2.

        1.5. **

        1.6. "Business Day" means a day that is not a Saturday, Sunday or a day
on which banking institutions in New York, New York or Geneva, Switzerland are
authorized by Law to remain closed.

        1.7. "Calendar Quarter" means each of the three-month periods ending on
March 31, June 30, September 30 and December 31 or, in the case of any partial
calendar quarter, the remaining part thereof during the Term. Except with
respect to Section 5.14, the first Calendar Quarter hereunder shall be the
period from the Effective Date until June 30, 2003.

        1.8. "Calendar Year" means a calendar year during the Term or, in the
case of any partial calendar year, the remaining part thereof during the Term.

        1.9. "Chargebacks" means credits, chargebacks, reimbursements,
administrative fees and other payments to wholesalers and other distributors,
group purchasing organizations, insurers and other institutions.

----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -2-
<PAGE>


        1.10. "Clinical Trial" means a clinical trial of the Product in the
Field for the Territory, including an investigator-sponsored clinical trial,
described in the Oncology Marketing Plan. Clinical Trials shall include the
Ongoing Clinical Trials.

        1.11. "Code" or "Codes" means the Code on Interactions with Healthcare
Professionals promulgated by the Pharmaceutical Research and Manufacturers of
America (PhRMA) and the American Medical Association (AMA) Guidelines on Gifts
to Physicians from Industry, as either of the foregoing may be amended from time
to time.

        1.12. "Commercially Reasonable Efforts" means the level of efforts and
resources required to promote a Product in the Territory in a sustained manner
consistent with the efforts a similarly situated company would typically devote
to a product of similar sales potential or strategic value resulting from its
own research efforts, based on conditions then prevailing.

        1.13. "Commission Payment" shall have the meaning set forth in Section
6.6.

        1.14. "Confidential Information" means all confidential materials, data
or other information, including any proprietary information (whether or not
patentable, or protectable as a trade secret), regarding a party's technology,
products, business or objectives that is disclosed to the other party pursuant
to this Agreement. All information disclosed prior to the Effective Date by
Serono or its Affiliates to OSI under or pursuant to the Confidentiality
Agreement between Serono International S.A. and OSI dated 5 December 2002 (the
"CDA") shall be deemed "Confidential Information" of Serono. All information
disclosed prior to the Effective Date by OSI or its Affiliates to Serono under
or pursuant to the CDA shall be deemed "Confidential Information" of OSI.
Excluded from the foregoing definition of Confidential Information is such
information that:


                                      -3-
<PAGE>

                (a) was known by the receiving party or its Affiliates prior to
its date of disclosure to the receiving party as shown by the receiving party's
or its Affiliates' written records;

                (b) either before or after the date of the disclosure to the
receiving party is lawfully disclosed to the receiving party or its Affiliates
by third parties who had a legal right to disclose the same;

                (c) either before or after the date of the disclosure to the
receiving party becomes published or generally known to the public through no
fault or omission on the part of the receiving party or its Affiliates;

                (d) is independently developed by or for the receiving party or
its Affiliates without reference to or reliance upon the Confidential
Information; or

                (e) is required to be disclosed by the receiving party to comply
with applicable Laws, including the Act, or court orders and to defend or
prosecute litigation; provided, however, that the receiving party shall, to the
extent permitted by such Laws, order or process, first have given prompt notice
to the disclosing party to enable it to seek any available exemptions from or
limitations on such disclosure requirement and shall reasonably cooperate in
such efforts by the disclosing party, at the disclosing party's sole expense.

        1.15. "Control" means the legal authority or right of a party to grant a
license or sublicense of intellectual property rights to another party or to
otherwise disclose proprietary or trade secret information to such other party,
without breaching the terms of any agreement with a third party or
misappropriating the proprietary or trade secret information of a third party.

        1.16. "Copyrights" means the copyrights in works of authorship related
to the Product in the Field in the Territory that Serono or one its Affiliates
Control, together with any registrations and applications for registration
thereof.


                                      -4-
<PAGE>

        1.17. "Detail" means a face-to-face meeting (including live video
presentation) with a physician; other medical professional with prescribing
authority; or office nurse or medical paraprofessional with influence over
pharmaceutical prescribing or treatment regimes for patients in the Territory
during which scientific and/or medical information about the Product in the
Field is discussed. A Detail does not include a reminder or sample drop. When
used as a verb, the term "Detailing" means to engage in the activity of a
Detail.

        1.18. "Effective Date" means the date as of which this Agreement is
entered into as first set forth above.

        1.19. "FDA" means the United States Food and Drug Administration and any
successor agency thereto.

        1.20. "Field" means the treatment of humans for all indications within
the field of oncology.

        1.21. "First Generic Date" means the date that a first third party makes
a product containing mitoxantrone available for sale in the Territory after
receiving approval from the FDA to market such product in the Territory **.

        1.22. "Governmental Authority" means any court, agency, department or
other instrumentality of any federal, state, county, city or other political
subdivision.

        1.23. "IMS" shall mean IMS Health and its Affiliates.

        1.24. "Indemnified Party" shall have the meaning set forth in Section
10.5.

        1.25. "Indemnifying Party" shall have the meaning set forth in Section
10.5.


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -5-
<PAGE>

        1.26. "Initial Period" shall have the meaning set forth in Section
2.2.2.

        1.27. "Joint Management Committee" or "JMC" means the committee
established pursuant to Section 3.1.

        1.28. "Know-How" shall have the meaning set forth in Section 8.3.

        1.29. "Law" or "Laws" means all laws, statutes, rules, regulations,
orders, judgments and/or ordinances of any Governmental Authority in the
Territory.

        1.30. "License Agreement" means the License and Commercialization
Agreement by and between Immunex Corporation and Serono dated November 12, 2002.

        1.31. "Licensed Technology" means the Patent, the Trademark, the
Copyrights and the Know-How.

        1.32. "Losses" means any and all (i) losses, liabilities, damages,
fines, royalties, governmental penalties, obligations, deficiencies, interest,
awards, settlements and judgments, and (ii) costs and expenses and disbursements
(including reasonable attorneys' fees and expenses) reasonably incurred in
investigating, preparing or defending any claim, action, suit or proceeding,
commenced or threatened.

        1.33. "Maintenance Term" **.

        1.34. "Manufacturing Agreement" means the contract for the manufacture
and supply of the Product between Serono or one of its Affiliates and a
third-party manufacturer, as such contract may be amended or replaced from time
to time.


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -6-
<PAGE>

        1.35. "Medical Science Liaison" means an individual employed by OSI to
perform MSL Activities.

        1.36. "MSL Activities" means through the use of Medical Science Liaisons
the maintenance of effective relationships with clinical investigators with
respect to the Product in the Field in the Territory. MSL Activities would also
include responding to physicians' requests for medical information with respect
to the Field.

        1.37. "MS Marketing Plan" means the plan for Serono's promotion and
detailing of the Product in the Territory in the field of multiple sclerosis.

        1.38. "NDA" means New Drug Application No. 19-297 filed with the FDA
with respect to the Product.

        1.39. "Net Sales" means the gross amounts invoiced for the sale of the
Product in the Field in the Territory to independent third parties as determined
in accordance with Section 6.5, less (to the extent specifically included in the
gross amounts invoiced and not already deducted therefrom ) (i) normal and
customary returns and allowances (actually paid, or actually estimated under
accounting policies and procedures in accordance with International Accounting
Standards or U.S. generally accepted accounting principles, consistently
applied), including prompt payment and volume discounts, price reductions
(including Rebates) and Chargebacks, whether in the form of cash, a credit or
free replacements (in which case the amount to be deducted from the gross
amounts invoiced shall be the cost of the replacements to Serono); (ii)
applicable outbound transportation, importation, insurance or other handling
charges, and any duties or other governmental charges imposed upon the
importation, use or sale of the Product; (iii) any sales, excise, value added or
similar taxes (not including income taxes); (iv) the actual acquisition cost of
devices used for dispensing or administering the Product and that accompany


                                      -7-
<PAGE>

the Product as it is sold; (v) amounts debited on account of bad debts with
respect to sales previously invoiced as set forth in this Section 1.39; and (vi)
**. The transfer of Product by Serono or one of its Affiliates to another
Affiliate shall not be considered a sale. Disposal of Product for, or use of
Product in, clinical or pre-clinical trials or as free samples shall not give
rise to any deemed sale under this Section 1.39.

        1.40. "Non-Breaching Party" shall have the meaning set forth in Section
11.2.

        1.41. "Oncology Marketing Plan" means the plan for OSI's Promotion and
Detailing of the Product and the conduct of MSL Activities and clinical trials
as described in Section 2.2 hereof.

        1.42. "Ongoing Clinical Trials" means the clinical trials of the Product
in the Field in the Territory that are described in Exhibit A hereto.

        1.43. "OSI Parties" shall have the meaning set forth in Section 10.3.1.

        1.44. "Patent" means U.S. Patent No. 4,820,738.

        1.45. "PDMA" shall have the meaning set forth in Section 2.11.2

        1.46. "Primary Detail" means a Detail in which the Product is given
significant emphasis which shall not be less than the emphasis given to other
products.

        1.47. "Product" means the product containing mitoxantrone hydrochloride
that is sold by Serono under the trademark Novantrone(R) as of the Effective
Date, including modifications to the product that are covered by the NDA (as
modified from time to time, other than modifications that cover new formulations
of the product).


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -8-
<PAGE>

        1.48. "Product Labeling" means (i) the FDA approved full prescribing
information for the Product, including any required patient information, and
(ii) all labels and other written, printed, or graphic matter upon any
container, wrapper, or any package insert, utilized with or for the Product.

        1.49. "Promote" or "Promotion" means performing those activities and
obligations that are intended to encourage sales of the Product in the Field in
the Territory and are described in the Oncology Marketing Plan, including market
research, journal advertising, direct mail programs, direct-to-consumer
advertising, and participation in trade shows, symposia, congresses and other
medical meetings; provided, however, such activities and obligations shall not
include Detailing and the conduct of Clinical Trials or MSL Activities.

        1.50. "Promotional Materials" means all written, printed, graphic,
electronic, audio or video matter, including journal advertisements, sales
visual aids, direct mail, direct-to-consumer advertising, web pages, web links,
Internet postings, broadcast advertisements, sales reminder aids (e.g., scratch
pads, pens and other such items) and reprints intended for use or used by OSI in
connection with any Promotion or Detailing, except the Product Labeling.

        1.51. "Rebates" means rebates to state Medicaid and other governmental
programs and to health plans, insurance companies, mail service pharmacies and
other health care providers and payers.

        1.52. "Sales Representative" means an individual employed by OSI or
whose services are contracted for by OSI and who engages in Detailing and
Promotion.

        1.53. **

        1.54. "Secondary Detail" means a Detail other than a Primary Detail.


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -9-
<PAGE>

        1.55. "Serono Parties" shall have the meaning set forth in Section
10.4.1.

        1.56. "Standards" means the Accreditation Council for Continuing Medical
Education (ACCME) Standards for Commercial Support of Continuing Medical
Education, as they may be amended from time to time.

        1.57. "Term" means the period from the Effective Date until December 31,
2017, unless sooner terminated as provided in this Agreement.

        1.58. "Territory" means the United States of America, including its
territories and possessions.

        1.59. "Third Party Claims" shall have the meaning set forth in Section
10.3.1.


        1.60. "Trademark" means the trademark Novantrone(R) associated with the
Product, and/or any other trademark associated with the Product in the Field in
the Territory that may be selected and owned by Serono or one of its Affiliates.

        1.61. "Valid Claim" means an unexpired claim of the Patent that has not
lapsed or been abandoned; been disclaimed, denied or admitted to be
unpatentable, invalid or unenforceable through reissue, reexamination, or
disclaimer; or been found to be unpatentable, invalid or unenforceable by a
court or other authority in the United States, from which decision no appeal is
taken or can be taken.

        Whenever in this Agreement the terms "includes" or "including" are used,
unless expressly limited, such terms shall be without limitation to the
enumerated or listed items.


                                      -10-
<PAGE>

                                   ARTICLE II
                        OSI'S RIGHTS AND RESPONSIBILITIES

        2.1. Grant of Rights. Subject to the terms and conditions of this
Agreement, Serono grants to OSI under the Licensed Technology the exclusive
right during the Term to Promote, Detail and provide MSL Activities for the
Product in the Field in the Territory and to conduct the Clinical Trials. The
terms, conditions and obligations of this grant of rights are subject to the
terms and conditions of, and the obligations of Serono pursuant to, the License
Agreement.

        2.2. Oncology Marketing.

                2.2.1 Oncology Marketing Plan. OSI will prepare the Oncology
Marketing Plan for Calendar Year 2003 for submission to the JMC for its review
and approval within sixty (60) days of Effective Date. For each subsequent
Calendar Year, OSI will prepare the Oncology Marketing Plan for submission to
the JMC for its review and approval no later than thirty (30) days after the
beginning of each such Calendar Year. The Oncology Marketing Plan will include
strategic objectives and plans for promoting the Product in the Field in the
Territory; the projected number of Primary Details and Secondary Details
intended to be performed in each Calendar Quarter; a priority call list of
physicians on whom OSI intends the Sales Representatives to call for Detailing;
clinical trial strategies and plans; strategies for the conduct of MSL
Activities; and forecasts, including an annual sales forecast for the Product in
the Field for the upcoming Calendar Year as well as the four (4) Calendar Years
thereafter (i.e., a running 5-year sales forecast) as well as forecasts for
Clinical Trial supplies and Product samples for the upcoming Calendar Year.

                2.2.2 Oncology Marketing Efforts. OSI shall use Commercially
Reasonable Efforts to promote the Product, to maximize sales of the Product and
to achieve the objectives set forth in the Oncology Marketing Plan and such
efforts shall not be diminished in the event that OSI markets any other product
in the Field. In particular, OSI shall begin Promotion and


                                      -11-
<PAGE>

Detailing of the Product as soon as practicable ** (the "Initial Period") and
shall deploy sufficient Sales Representatives for Promotion and Detailing of the
Product.

        2.3. Compliance.

                2.3.1 Law, Codes and this Agreement. OSI shall Promote and
Detail the Product and conduct the Clinical Trials and the MSL Activities in
accordance with applicable Law, the Codes, the terms of this Agreement, and the
then-current Oncology Marketing Plan. OSI shall promptly notify Serono of and
provide Serono with a copy of any correspondence or other reports with respect
to the Promotion and Detailing of the Product or the conduct of Clinical Trials
or MSL Activities that OSI receives from any Governmental Authority, including
the FDA or from the Pharmaceutical Research and Manufacturers of America (PhRMA)
or the American Medical Association (AMA) relating to its compliance with
applicable Law or the Codes.

                2.3.2 Standards. OSI shall Promote the Product and conduct the
MSL Activities in conformity with the practices and procedures relating to the
education of the medical community set forth in the Standards. OSI shall
promptly notify Serono of and provide Serono with a copy of any correspondence
or other reports with respect to the Promotion of the Product or the conduct of
the MSL Activities that OSI receives from the Accreditation Council for
Continuing Medical Education (ACCME) relating to its compliance with the
Standards.

                2.3.3 Product Labeling and Promotional Materials. In connection
with OSI's Promotion and Detailing of the Product, OSI shall not make, nor
permit the Sales Representatives to make, any statement, representation or
warranty, oral or written, to any third party that is inconsistent with the
Product Labeling or the Promotional Materials. OSI shall promptly notify Serono
of and provide Serono with a copy of any correspondence or other


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -12-
<PAGE>

reports or complaints received by OSI from any Governmental Authority, including
the FDA, or any third party claiming that any Promotional Materials are
inconsistent with the Product Labeling or are otherwise in violation of the Act.

                2.3.4 Debarment Limitations. In the course of Promoting and
Detailing the Product and conducting the MSL Activities and the Clinical Trials,
OSI shall not knowingly use any employee or consultant who is or has been
debarred by the FDA or any counterpart of the FDA outside the United States or,
to the best of OSI's knowledge, is or has been the subject of debarment
proceedings by any such regulatory authority. OSI shall promptly notify Serono
of and provide Serono with a copy of any correspondence or other reports with
respect to any use of a debarred employee or consultant in connection with OSI's
performance of its obligations under this Agreement that OSI receives from any
third party.

                2.3.5 Intellectual Property Rights. In the course of Promoting
and Detailing the Product and conducting the MSL Activities and the Clinical
Trials, OSI shall not misappropriate any trade secret or other intellectual
property of a third party. OSI shall promptly notify Serono of and provide
Serono with a copy of any correspondence or other reports with respect to any
alleged misappropriation of a third party's intellectual property in connection
with OSI's performance of its obligations under this Agreement that OSI receives
from any third party.

        2.4. Sales Representatives.

                2.4.1 Qualifications. OSI agrees that throughout the Term it
shall Promote and Detail the Product using only Sales Representatives who
specialize, among other things, in detailing ethical pharmaceutical products to
physicians and who have relevant experience. OSI shall require each Sales
Representative to attend sales training for the Product as described in Section
2.7.2 before such Sales Representative is permitted to Promote or Detail the
Product.


                                      -13-
<PAGE>

                2.4.2 Compensation. OSI shall be solely responsible for all
costs and expenses of compensating the Sales Representatives. To the extent
permitted under applicable Laws, OSI shall pay incentive compensation to the
Sales Representatives pursuant to an incentive compensation plan that determines
the target payment for the Product in a manner that would reasonably be expected
to cause the Sales Representatives to promote the Product with at least the same
degree of effort that they use for the promotion of other pharmaceutical
products of similar sales potential or strategic importance. OSI shall notify
the Sales Representatives prior to beginning Detailing for the Product of the
total potential incentive compensation. Promptly after the adoption by OSI of an
incentive compensation payment plan with respect to the Product pursuant to this
Agreement and any material amendments thereto, OSI shall provide to the JMC a
summary of the methodology used by OSI to make incentive compensation payments
for the Product pursuant to such plan.

        2.5. Marketing Management Team. OSI shall assemble a marketing
management team whose responsibility shall be to coordinate and manage the
implementation of the Oncology Marketing Plan.

        2.6. Medical Science Liaisons. OSI agrees that throughout the Term it
shall conduct MSL Activities using only Medical Science Liaisons who have
sufficient technical training and experience to perform such activities in a
manner consistent with the practice by leading pharmaceutical and biotechnology
companies of such activities within the Field. OSI shall require each Medical
Science Liaison to attend training as described in Section 2.7.3 before such
Medical Science Liaison is permitted to conduct MSL Activities.

        2.7. Training.

                2.7.1 Training Materials. Within ten (10) days after the
Effective Date, Serono shall provide to OSI, at no cost, a mutually agreed
number of the training materials received by Serono pursuant to the License
Agreement that are appropriate to train Sales Representatives to


                                      -14-
<PAGE>

Promote and Detail the Product and to train Medical Science Liaisons to conduct
MSL Activities, including an electronic copy thereof, if available. OSI shall be
permitted, at its own expense, to develop training materials for its Sales
Representatives or Medical Science Liaisons in other media or forms provided
that such materials are approved by Serono pursuant to Section 5.3. Except with
respect to training materials developed or created by or for OSI that relate to
the Field in general and not to the Product (which shall be owned by OSI),
Serono shall own all rights to all training materials, including all copyrights
thereto. OSI shall send such training materials to Serono for review and
approval pursuant to Section 5.3. Within thirty (30) days after the termination
or expiration of this Agreement, OSI shall return, or otherwise dispose of in
accordance with instructions from Serono, all training materials owned by Serono
and will provide Serono with a certified statement that all such training
materials have been returned or otherwise properly disposed of.

                2.7.2 Training Sales Representatives. OSI shall, at its own
expense, train its Sales Representatives using the training materials described
in Section 2.7.1, the Promotional Materials and such programs as OSI shall deem
appropriate that are in compliance with OSI's obligations hereunder and have
been approved by the JMC. Such programs shall include training with respect to
reporting adverse drug experiences and technical complaints. After the initial
training, OSI shall periodically provide additional training to each Sales
Representative, in accordance with OSI's training requirements and training
programs that are approved by the JMC and using training materials that are
approved by Serono.

                2.7.3 Training Medical Science Liaisons. OSI shall, at its own
expense, train its Medical Science Liaisons using the training materials
described in Section 2.7.1 and such programs as OSI shall deem appropriate that
are in compliance with OSI's obligations hereunder and have been approved by the
JMC. After the initial training, OSI shall periodically provide additional
training to each Medical Science Liaison, in accordance with OSI's training



                                      -15-
<PAGE>

requirements and training programs that are approved by the JMC and using
training materials that are approved by Serono.

                2.7.4 Training Marketing Management. OSI shall also, at its own
expense, train its marketing management team using such training materials and
programs as OSI shall deem appropriate that are in compliance with OSI's
obligations hereunder.

                2.7.5 Communications to Sales Representatives and Medical
Science Liaisons. OSI shall provide Serono with copies of general communications
(including communications sent electronically or by voice mail) disseminated by
OSI to the Sales Representatives and Medical Science Liaisons and relating to
strategies for the Promotion or Detailing of the Product or the conduct of MSL
Activities, as applicable.

        2.8. National Launch Meeting and Periodic Sales Meetings. The parties
intend that OSI will hold a national launch meeting and periodic sales meetings
for the Product. Serono shall determine which, if any, of its employees and
invitees shall attend such national launch meeting and periodic sales meetings.
All such employees and invitees shall attend such activities at Serono's sole
expense.

        2.9. Detailing. OSI shall perform during each Calendar Quarter the
number of Primary Details and Secondary Details in accordance with the Oncology
Marketing Plan.

        2.10. Promotional Materials. Within thirty (30) days after the Effective
Date, Serono shall provide to OSI at Serono's acquisition cost a mutually agreed
number of copies of the Promotional Materials received by Serono pursuant to the
License Agreement that are appropriate for the Promotion of the Product,
including an electronic copy thereof, if available. Serono shall invoice OSI for
the acquisition cost of such Promotional Materials at the time such materials
are provided to OSI and OSI shall pay such invoice within thirty (30) days after
its receipt of such invoice. OSI shall Promote and Detail the Product using only
the Promotional


                                      -16-
<PAGE>

Materials and no other promotional, advertising, communication or educational
materials. Subject to Serono's approval pursuant to Section 5.3, OSI shall be
responsible for the creation, preparation, production and reproduction of all
other Promotional Materials, at its own expense. With the exception of any
Promotional Materials created or developed by or for OSI that relate to the
Field in general and not to the Product (which shall be owned by OSI), Serono
shall own all rights to all Promotional Materials, including all copyrights
thereto. Unless and until Promotional Materials are approved by Serono for
publication or other general dissemination, OSI shall maintain them in
confidence pursuant to the terms of Article IX and shall not use them in
Promoting or Detailing the Product. OSI shall send the Promotional Materials to
Serono for review and approval pursuant to Section 5.3. OSI shall at all times
during the Term provide Serono with five (5) final copies of all Promotional
Materials concurrently with OSI's initial public dissemination thereof, and such
additional copies as may be reasonably requested by Serono from time to time.
Within thirty (30) days after the termination or expiration of this Agreement,
OSI shall return, or otherwise dispose of in accordance with instructions from
Serono, all Promotional Materials owned by Serono and will provide Serono with a
certified statement that all such Promotional Materials have been returned or
otherwise properly disposed of.

        2.11. Samples.

                2.11.1 Supply. In support of OSI's Promotion of the Product
hereunder, Serono shall supply OSI with Product samples in accordance with the
forecasts for the supply of Product samples established by the then-current
Oncology Marketing Plan. Serono shall ship such samples to a central location
designated by OSI.

                2.11.2 Use. OSI shall use Product samples strictly in accordance
with the then-current Oncology Marketing Plan and shall store and distribute
such samples in full compliance with all applicable Laws, including the
requirements of the Prescription Drug Marketing Act of


                                      -17-
<PAGE>

1987, as amended (the "PDMA"). OSI will maintain those records required by the
PDMA and all other Laws and shall allow representatives of Serono to inspect
such records and storage facilities for the Product samples during regular
business hours on request with reasonable prior notice, but not more than once
per Calendar Year, unless Serono has a reasonable cause to be concerned about
compliance of such records or storage facilities with applicable Laws or the
terms of this Agreement. Subject to receipt of necessary information from OSI on
a timely basis, Serono shall be solely responsible for the filing of any
necessary reports to the FDA in connection with the PDMA, and OSI agrees to
provide Serono with any information in OSI's control that is required by the
PDMA to be included in such filings.

                2.11.3 Cost. Serono shall supply Product samples to OSI at
Serono's (i) out-of-pocket cost for the purchase of such samples plus ** and
(ii) out-of-pocket cost for the shipment such samples, which amounts shall be
invoiced to OSI and shall be payable by OSI within thirty (30) days after the
date of invoice.

                2.11.4 Return of Samples. Within thirty (30) days after the
termination or expiration of this Agreement, OSI shall return, or otherwise
dispose of in accordance with instructions from Serono, all remaining Product
samples and will provide Serono with a certified statement that all remaining
Product samples have been returned or otherwise properly disposed of.

        2.12. Clinical Trials.

                2.12.1 Conduct. OSI shall conduct the Clinical Trials in
accordance with the then-current Oncology Marketing Plan, including by
performing the obligations of Serono under the contracts for the Ongoing
Clinical Trials and by contracting with third parties to perform the other
Clinical Trials. Without the prior written approval of Serono, which approval
shall not be


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -18-
<PAGE>

unreasonably withheld, OSI shall not conduct, sponsor or support any
pre-clinical or clinical studies of the Product or make any clinical grants or
donations with respect to the Product other than the Clinical Trials. After the
Effective Date, OSI shall be responsible for all rights and obligations of
Serono under the contracts for the Ongoing Clinical Trials, except to the extent
such rights and obligations relate to periods on or prior to the Effective Date;
**. As soon as is reasonably practical after the Effective Date, Serono will
assign and transfer to OSI the contracts for the Ongoing Clinical Trials. To the
extent any contract for the Ongoing Clinical Trials is not assignable by Serono,
such contract shall be retained by Serono; provided, however, that OSI shall
reimburse Serono for any applicable fees or other payments payable to third
parties after the Effective Date pursuant to such contracts and the cost of any
Product samples provided pursuant to such contracts after the Effective Date.
Serono shall approve a template for any contracts for Clinical Trials and
further approval will not be required in connection with such contracts, unless
there are material changes to such template; provided, however, that any
material changes to the template specifically approved by Serono for subsequent
use will not require any further approval by Serono. OSI agrees that, in its
conduct of the Clinical Trials, it will not infringe any trademarks, know-how,
patent rights, or other intellectual property rights of any third party. In
addition, without the prior written approval of Serono, OSI shall not conduct,
sponsor or support any Clinical Trials that would reasonably be expected to have
an adverse effect on Serono's development, promotion or sale of the Product
outside the Field.

                2.12.2 Regulatory Compliance. The parties will reasonably
cooperate to make any appropriate arrangements in accordance with the Law to
permit OSI to conduct the Clinical Trials. OSI will establish such systems and
maintain such records as required to conduct the Clinical Trials in accordance
with the Act and all other applicable Laws and shall allow representatives of
Serono to inspect such systems and records during regular business hours on


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -19-
<PAGE>

request with reasonable prior notice, but not more than once per Calendar Year,
unless Serono has a reasonable cause to be concerned about compliance of such
systems and records with applicable Laws or the terms of this Agreement.

                2.12.3 Rights under Clinical Trial Contracts. As between OSI and
Serono, Serono shall have all right, title and interest in and to any data,
results or other information relating to the Product and arising from the
Clinical Trials; provided, however, OSI shall have the right to use any
publications or oral or written presentations of any such data, results or other
information that Serono Controls in connection with its Promotion, Detailing or
conduct of MSL Activities in accordance with the terms of this Agreement. OSI
hereby assigns and transfers to Serono all right, title and interest that OSI
may hereafter acquire pursuant to contracts for the Clinical Trials in and to
any data, results or other information relating to the Product. OSI shall use
its commercially reasonable efforts not to permit any publication or oral or
written presentation of such data, results or other information without the
prior written approval of Serono, which shall not be unreasonably withheld, and
shall provide Serono the opportunity to review any proposed publication or
presentation at least fifty (50) days prior to its intended presentation or
submission for publication. If by the end of the foregoing period, comment or
approval from Serono has not been received by OSI, then Serono's approval shall
be deemed given.

                2.12.4 Costs. OSI shall bear all costs of the Clinical Trials
after the Effective Date, including any applicable fees or other payments
payable to third parties pursuant to contracts for the Clinical Trials. OSI
shall purchase the Product for the conduct of the Clinical Trials from Serono in
accordance with the forecasts for Clinical Trial supplies established by the
then-current Oncology Marketing Plan. Serono shall supply such Product to OSI at
Serono's (i) out-of-pocket cost for the purchase of such Product plus ** and
(ii) out-of-pocket cost for the


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -20-
<PAGE>

shipment of such Product, which amounts shall be invoiced to OSI and shall be
payable by OSI within thirty (30) days after the date of invoice. Serono shall
ship such Product to a central location designated by OSI.

        2.13. Promotional Activities.

                2.13.1 Conduct. OSI shall conduct the Promotional activities for
the Product set forth in the then-current Oncology Marketing Plan.

                2.13.2 Cost. OSI shall bear the cost of conducting all
Promotional activities described in Section 2.13.1 hereof.

        2.14. MSL Activities.

                2.14.1 Conduct. OSI shall conduct the MSL Activities set forth
in the then-current Oncology Marketing Plan. In the course of conducting the MSL
Activities, OSI shall distribute to physicians only those materials that have
been submitted to Serono for review and approval hereunder and no other
materials. OSI shall send such materials to Serono for review and approval
pursuant to Section 5.3.

                2.14.2 Cost. OSI shall bear the cost of conducting all MSL
Activities described in Section 2.14.1 hereof.

        2.15. Activities Reports. Within thirty (30) days after the end of each
Calendar Quarter during the Term, OSI shall provide the JMC with a written
report (an "Activities Report") summarizing in reasonable detail the material
activities undertaken by OSI during such Calendar Quarter in connection with the
Oncology Marketing Plan, including the number and type of Details made by the
Sales Representatives during such Calendar Quarter, and the information acquired
by OSI with respect to the Product during such Calendar Quarter, to the extent
OSI is not prohibited by Law or contractual obligations from disclosing such
information, including


                                      -21-
<PAGE>

market information relating to developments in the Field, competing products,
acceptance of the Product, complaints and similar information.

        2.16. Communication. OSI shall have the right to arrange for its
employees and outside consultants directly involved in the co-promotion of the
Product to visit Serono or its Affiliates at their offices, and to discuss
related activities with the technical and business personnel and consultants of
Serono or its Affiliates, provided that such visits shall be upon reasonable
prior notice to Serono or its Affiliates and during normal business hours and
shall not unreasonably interrupt the operations of Serono or its Affiliates.

                                   ARTICLE III
                           MANAGEMENT OF CO-PROMOTION

        3.1. Joint Management Committee. In order to fulfill the objectives of
this Agreement, the parties agree within thirty (30) days of the Effective Date
to establish a Joint Management Committee to manage the co-promotion
collaboration established hereby. The goal of the JMC will be to coordinate the
activities of the parties so as to enhance the ability of each party to carry
out its strategic objectives for the promotion of the Product outside the Field
and within the Field, respectively, in accordance with the terms and conditions
of this Agreement while minimizing duplication of efforts and potential
conflicts between the parties. The parties acknowledge the potential importance
of maintaining multiple active lines of communication, as well as working
together to avoid unforeseen obstacles. Each party shall designate three (3)
members of the JMC who shall have the requisite expertise and ability to manage
this co-promotion collaboration. Either party may replace any of its designated
members of the JMC from time to time upon written notice to the other party.

        3.2. Meetings. The JMC shall meet at least quarterly, or with such other
frequency as may be established by the JMC from time to time. The meetings may
be held in person, by telephone, or by video conference call. A reasonable
period in advance of each such meeting,


                                      -22-
<PAGE>

OSI shall prepare the initial draft of an agenda for the meeting and shall
submit the draft to Serono for comments. Each party shall use commercially
reasonable efforts to cause its members of the JMC to attend each meeting.
Meetings of the JMC may be held only if a quorum of at least two (2) members
appointed by each party participate. The location of the meetings of the JMC
shall alternate between the offices of the parties, unless otherwise agreed by
the parties. Additional participants may be invited by any member to attend
meetings where appropriate. Such additional participants shall not be deemed to
have any of the rights or responsibilities of a member of the JMC. Following the
meeting, OSI shall promptly circulate to the members of the JMC the minutes of
the meeting for review, comment and ratification. Each party shall bear its own
travel and related costs incurred in connection with participation in the JMC.

        3.3. Decision Making. The decisions of the JMC shall be made by majority
vote, with the members of each party entitled to one (1) vote. The parties shall
cause their respective members of the JMC to use diligent efforts, acting in
good faith, to resolve all matters presented to them as expeditiously as
possible. Any matters that the JMC is unable to resolve will be resolved through
the dispute resolution process set forth in Article XIII.

        3.4. Responsibilities. The responsibilities of the JMC shall include:

                (a) reviewing and approving the strategic objectives and goals
of the Oncology Marketing Plan and the implementation thereof;

                (b) reviewing the MS Marketing Plan and Oncology Marketing Plan
to identify potential opportunities for cooperation and to attempt to avoid
duplication of efforts and conflicts;

                (c) updating, on a Calendar Quarter basis, the forecasts in the
Oncology Marketing Plan for Product, Product samples and Clinical Trial supplies
for the twelve (12) month period immediately following such Calendar Quarter;


                                      -23-
<PAGE>

                (d) formulating strategic objectives with respect to pricing and
discounting of the Product (provided that Serono shall make, with due
consideration for the potential effect on Net Sales, all final decisions as to
pricing and discounting of the Product);

                (e) approving strategies for promoting the Product to and
contracting with Governmental Authorities, group purchasing organizations,
health insurance providers, health plans, pharmacies and other appropriate
entities (provided that only Serono shall have the right to contract with such
bodies);

                (f) reviewing and approving the parameters and scope of the
indigent patient program described in Section 5.17 hereof;

                (g) facilitating the coordination of the call centers maintained
by each party to respond to medical, consumer and other inquiries as
contemplated in Section 4.8 hereof;

                (h) reviewing training programs for use by OSI to train Sales
Representatives and Medical Science Liaisons to ensure consistency with the
terms and conditions of this Agreement; and

                (i) reviewing the progress and results of Clinical Trials and
OSI's strategies for the communication of any such results.

        3.5. Retention of Rights. Notwithstanding the foregoing, each party
shall retain the rights, powers, and discretion expressly granted to it under
this Agreement, and the JMC shall not be delegated or vested with any such
rights, powers or discretion except as expressly provided in this Agreement. The
JMC shall not have the power to amend or modify this Agreement, which may only
be amended or modified as provided in Section 14.7 hereof.


                                      -24-
<PAGE>

                                   ARTICLE IV
                               REGULATORY MATTERS

        4.1. Regulatory Approvals. All regulatory approvals within the Territory
relating to the Product, including the NDA, shall be deemed the property of
Serono or one of its Affiliates and held in the name of Serono or one of its
Affiliates. As between Serono and OSI, Serono shall have the exclusive
responsibility and final authority for all matters relating to the nature and
content of the NDA or other regulatory filings submitted to the FDA or other
Governmental Authority concerning the Product. Serono agrees to use commercially
reasonable efforts to maintain the NDA (as it may be modified from time to time)
throughout the Term in accordance with applicable Law.

        4.2. Communications with the FDA. Serono shall have the sole
responsibility for communicating with the FDA and other Governmental Authorities
about the Product. A copy of all such Material written communications related to
the Product shall be promptly forwarded by Serono to OSI. For purposes of this
Section 4.2 and Section 4.3, a "Material" communication or submission is a
communication or submission that could affect the Product Labeling with respect
to the Field, adversely affect the supply or approval status of the Product,
interfere with OSI's ability to Promote and Detail the Product, or relates to
the conduct of the Clinical Trials.

        4.3. Submissions to the FDA. Except for the proprietary Chemistry,
Manufacturing and Controls (CMC) portion of the NDA, Serono shall use
commercially reasonable efforts to provide to OSI a copy of Material submissions
to the FDA related to the Product reasonably in advance of their submission.
Serono shall give due consideration to any comments timely received from OSI
relating to such submission.

        4.4. Investigations. To the extent known by Serono and permitted by Law
or any contract by which Serono is bound, Serono shall promptly provide notice
to OSI and copies of any and all written communications concerning (i) the
initiation of any investigation, review or


                                      -25-
<PAGE>

inquiry by the FDA or other Governmental Authority relating to the Product,
including the manufacture, quality, labeling, sale, promotion, distribution, or
clinical investigation of the Product; (ii) the need for a remedial action
related to one or more batches of the Product (including a recall, market
withdrawal or correction); (iii) the initiation of a detention, seizure of or
injunction against distribution of the Product by the FDA or other Governmental
Authority; (iv) any Product-related inspection (other than routine inspections)
conducted by the FDA or other Governmental Authority of any clinical research
facility, manufacturing and quality control facility, distribution facility or
similar facility; or (v) the receipt of any complaint concerning suspected or
actual Product tampering or contamination.

        4.5. Recalls. Each party shall notify the other party promptly if any
batch or lot of the Product, or the Product itself, is alleged or proven to be
the subject of a recall, market withdrawal or correction in the Territory, and
the parties shall cooperate in the handling and disposition of such recall,
market withdrawal or correction; provided, however, that Serono shall, after
making reasonable efforts to consult with OSI, have the final authority with
respect to such matters. **

        4.6. OSI Notification. OSI shall notify Serono promptly after receiving
information about the initiation of any investigation, review or inquiry by the
FDA or other Governmental Authority concerning the manufacture, quality,
labeling, sale, promotion, distribution, or clinical investigation of the
Product.

        4.7. Adverse Drug Experiences and Technical Complaints. Reporting
adverse drug experiences and technical complaints with respect to the Product,
including those arising in connection with the conduct of the Clinical Trials,
shall be in accordance with Exhibit B.

        4.8. Inquiries. All medical, consumer and other inquiries (including
those related to patient promotion, fulfillment, patient assistance and other
programs or activities) concerning the


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -26-
<PAGE>

Product in the Field shall be addressed by OSI, provided that OSI shall forward
to Serono, to the attention of such person(s) as Serono shall designate, any
inquiries to which it cannot respond as well as any inquiries related to
indications outside the Field and any inquiries subject to the terms and
conditions of Section 4.7 hereof. Serono shall forward to OSI to the attention
of such person(s) as OSI shall designate, any such inquiries related to
indications within the Field. OSI shall prepare reports on at least a Calendar
Quarter basis describing the inquiries it has received and its responses
thereto. Promptly after the Effective Date, Serono shall provide OSI with all
material information known to Serono and in its possession that is relevant or
appropriate to enable OSI to respond promptly to medical questions or inquiries
related to the Product in the Field. Relevant new information with respect to
the Product in the Field of which Serono becomes aware shall be supplied to OSI
by Serono as it becomes available. OSI will establish such systems and maintain
such records as required to respond to such inquiries in accordance with the Act
and all other applicable Laws and shall allow representatives of Serono to
inspect such systems and records during regular business hours on request with
reasonable prior notice, but not more than twice per Calendar Year, unless
Serono has a reasonable cause to be concerned about compliance of such systems
and records with applicable Laws or the terms of this Agreement.

                                    ARTICLE V
                      SERONO'S RIGHTS AND RESPONSIBILITIES

        5.1. Product Pricing and Discounting. Subject to Sections 3.4(d) and
5.12, Serono shall have the right to determine the price of the Product and the
amount and circumstances in which that price may be discounted, if at all. OSI
shall not promote the Product by offering any prices or discounts other than
those established by Serono.

        5.2. Contracting with Organizations. Subject to Section 3.4(e), Serono
shall be responsible for contracting with those Governmental Authorities, group
purchasing


                                      -27-
<PAGE>

organizations, health insurance providers, health plans, pharmacies and other
bodies that it determines are appropriate for the promotion of the Product. OSI
shall not contract with any such authorities or organizations with respect to
the sale of the Product.

        5.3. Approval of Promotional Materials, Training Materials and Materials
used in the Conduct of MSL Activities. Serono shall approve, which approval
shall not be unreasonably withheld, all Promotional Materials prior to their use
by OSI in Promoting and Detailing the Product in accordance with Section 2.10.
Serono shall approve, which approval shall not be unreasonably withheld, all
training materials prior to their use by OSI in training Sales Representatives
and Medical Science Liaisons in accordance with Section 2.7. Serono shall
approve, which approval shall not be unreasonably withheld, all materials
distributed to physicians in the conduct of the MSL Activities prior to such
distribution in accordance with Section 2.14. Serono shall designate an employee
contact to whom OSI shall send for approval all Promotional Materials, training
materials and materials distributed to physicians in the conduct of the MSL
Activities. OSI shall send such materials to Serono for review only after
completion of full internal review and approval by OSI of such materials. Serono
shall notify OSI of its approval, or required changes with respect to such
materials within twenty (20) Business Days after Serono's receipt thereof.

        5.4. Distribution and Sales. Serono shall be responsible for the
distribution and sales of the Product in the Territory and shall book all sales
of the Product.

        5.5. Compliance with Codes and Standards. Serono shall promptly notify
OSI of and provide OSI with a copy of any correspondence or other reports with
respect to promotion of the Product received by Serono from either (i) the
Pharmaceutical Research and Manufacturers of America (PhRMA) or the American
Medical Association (AMA) relating to its compliance with the Codes or (ii) the
ACCME relating to its compliance with the Standards, which


                                      -28-
<PAGE>

correspondence or reports would be reasonably likely to have a significant
effect on OSI's ability to Promote or conduct the MSL Activities hereunder.

        5.6. Communication. Serono shall have the right to arrange for its
employees and outside consultants directly involved in the co-promotion of the
Product to visit OSI at its offices, and to discuss related activities with the
technical and business personnel and consultants of OSI, provided that such
visits shall be upon reasonable prior notice to OSI and during normal business
hours and shall not unreasonably interrupt the operations of OSI.

        5.7. Manufacturing Rights/Obligations. The parties understand and agree
that during the Term the Product will be manufactured by a third-party
manufacturer and supplied to Serono and the rights and obligations with respect
to such manufacture and supply will be as set forth in the Manufacturing
Agreement. Serono shall order Product samples and clinical supplies pursuant to
the Manufacturing Agreement in accordance with the forecasted demands for such
samples and clinical supplies set forth in the then-current Oncology Marketing
Plan, including any updates thereto pursuant to Section 3.4(c). When ordering
Product pursuant to the Manufacturing Agreement, Serono shall reasonably
consider the forecasted demands for Product set forth in the then-current
Oncology Marketing Plan, including any updates thereto pursuant to Section
3.4(c).

        5.8. NDA/Regulatory. Within thirty (30) days after the Effective Date,
Serono shall provide to OSI a copy of the NDA (except for the proprietary
Chemistry, Manufacturing and Controls (CMC) portion of the NDA).

        5.9. Product Supply. Serono shall use reasonable efforts to supply
enough Product to satisfy demand for the Product in the Territory. If, despite
such efforts to supply enough Product to satisfy such demand, there is not
enough Product to meet such demand, Serono and OSI shall meet to formulate a
plan for the allocation of the current supply of Product among purchasers.


                                      -29-
<PAGE>

        5.10. Inventory. Serono shall use commercially reasonable efforts to
maintain on an ongoing basis a safety stock of Product inventory equal to the
aggregate quantity of Product specified by the sales forecast in the Oncology
Marketing Plan and Serono's sales forecast outside the Field for **.

        5.11. Compliance. Serono hereby covenants that in connection with the
manufacture, sale and distribution of Product, Serono will comply with, and use
commercially reasonable efforts to assure that its suppliers comply with, all
applicable Law.

        5.12. **

        5.13. MS Marketing Plan. Serono will provide the MS Marketing Plan for
Calendar Year 2003 to the JMC within sixty (60) days of Effective Date. For each
subsequent Calendar Year, Serono will prepare the MS Marketing Plan and provide
it to the JMC no later than thirty (30) days after the beginning of each such
Calendar Year.

        5.14. Availability of Data. From time to time at the request of OSI, but
not more than once in any Calendar Quarter and only during the year following
the Effective Date, Serono shall make available to OSI, and Serono shall cause
its Affiliates to make available to OSI, during regular business hours and on
reasonable prior notice at Serono's facilities in Massachusetts, any information
obtained by Serono pursuant to the License Agreement related to the Product in
the Field that is relevant or appropriate to enable OSI to Promote and Detail
and conduct MSL Activities and Clinical Trials, but only to the extent that such
information has not already been supplied to OSI and that the provision of such
information is not already otherwise contemplated in this Agreement.


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -30-
<PAGE>

        5.15. Website. On any website relating solely to the Product that is
owned or controlled by, or operated on behalf of, Serono (including
www.novantrone.com, www.novantrone.net, www.novantrone.org,
www.mitoxantrone.com, www.mitoxantrone.net and www.mitoxantrone.org (the
"Websites"), Serono shall place (or cause to have placed) the OSI logo and
accompanying text provided by OSI, or such other OSI logo and accompanying text
as OSI may designate from time to time in writing to Serono, subject to review
and approval of any such text by Serono. Any such logo and accompanying text
shall be given appropriate placement on such websites and shall link to a
uniform resource locator ("URL") address designated by OSI, which URL address
may be changed by OSI from time to time upon reasonable notice to Serono;
provided, however, that before providing any such link to a URL address, Serono
shall have the right to review and approve the contents thereof. OSI grants
Serono the right to establish a link to the Websites or other websites
designated by Serono and approved by OSI from specific websites relating solely
to the Product owed or controlled by, or operated on behalf of, OSI. OSI also
grants Serono the right to place (or cause to have placed) the Serono logo and
accompanying text provided by Serono, or such other Serono logo and accompanying
text as Serono may designate from time to time in writing to OSI, on such OSI
websites, subject to review and approval of any such text by OSI.

        5.16. **

        5.17. Indigent Patient Program. Serono shall conduct an indigent patient
program with respect to the Product pursuant to terms that shall be submitted to
the JMC for review and comment. The parties acknowledge that Serono may conduct
such program using the services of a third-party vendor. OSI shall pay its
proportionate share of the Product supply and shipment costs and Serono's
reasonable cost of conducting such program, including labor, overhead and
out-of-pocket costs and expenses, based upon the proportion of patients
participating in such


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -31-
<PAGE>

program who are being treated for indications within the Field to the total
number of patients participating in such program. This amount shall be invoiced
to OSI at the end of each Calendar Quarter based on the conduct of such program
during the prior Calendar Quarter and shall be payable by OSI within thirty (30)
days after the date of invoice.

        5.18. Sales Report. Each week Serono shall provide to OSI a report of
the sales of the Product in the Territory for the prior week and year to date.

        5.19. IMS Data. At OSI's request, Serono shall make commercially
reasonable efforts to arrange for the provision to OSI of IMS DDD (drug
distribution data) related to the Product. OSI shall pay all costs Serono incurs
to secure and have such data provided to OSI; provided, however, that OSI shall
approve such costs in advance.

                                   ARTICLE VI
                                     PAYMENT

        6.1. Initial Fee. In consideration of the grant of rights hereunder and
in addition to the other payments provided for in this Agreement, OSI shall pay
to Serono, within ten (10) days of the Effective Date, a non-creditable and
nonrefundable initial fee of Forty-five Million Dollars ($45,000,000).

        6.2. Transition Services Fee. In consideration of Serono's agreement
pursuant to the terms of this Agreement to provide to OSI certain services
during the Initial Period, including providing Promotional Materials, training
materials and other materials and providing customer support services for the
Field, OSI shall pay to Serono, within ten (10) days of the Effective Date, a
non-creditable and nonrefundable transition services fee of Ten Million Dollars
($10,000,000).

        6.3. Maintenance Fee. In consideration of the ongoing rights to Promote
and Detail the Product hereunder during the Maintenance Term and in addition to
the other payments


                                      -32-
<PAGE>

provided for in this Agreement, OSI shall pay to Serono **, a non-creditable and
nonrefundable payment of **.

        6.4. Net Sales Report. Serono shall use commercially reasonable efforts
to deliver to OSI within forty-five (45) days, but in no event later than sixty
(60) days, after the end of each Calendar Quarter during the Term a report of
Net Sales during such Calendar Quarter and on a cumulative basis for the
applicable Calendar Year, including (i) an accounting of the deductions from Net
Sales permitted by the definition thereof, and (ii) adjustments, if any, to Net
Sales permitted by the definition thereof.

        6.5. Net Sales Determination. To determine Net Sales, Serono must
distinguish sales of the Product in the Field from sales of the Product outside
the Field. To distinguish such sales, Serono shall contract with a third-party
vendor, which third party vendor shall periodically, but no less often than each
Calendar Quarter, establish, as accurately as is reasonably possible, the
percentage of Product sales in the Field. Such percentage shall then be applied
in an appropriate manner to sales of the Product in the Territory to determine
Net Sales. Exhibit C describes a method for such measurement. The parties agree
that as soon as practicable after the Effective Date, and in any event within
thirty (30) days thereafter, they will review and, if necessary, optimize the
method described in Exhibit C; provided, however, that Serono shall have the
right finally to determine such method. Thereafter either party shall from time
to time have the right, upon written notice to the other party and following
consultation with the other party, to request a review of such method to ensure
its continuing accuracy and such review shall then be performed. Following the
performance of such review, Serono shall have the right finally to determine any
modifications to such method. The parties shall share equally the out-of-pocket
costs incurred by Serono in selecting and contracting with such third-party
vendor and performing any of the aforementioned reviews. This amount shall be
invoiced to OSI at the end


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -33-
<PAGE>

of each Calendar Quarter based on the costs incurred by Serono during the prior
Calendar Quarter and shall be payable by OSI within thirty (30) days after the
date of invoice. The determination of the third party as to the sales of the
Product in the Field shall be final and binding on the parties, absent manifest
error, and shall not be subject to audit under this Agreement.

        6.6. Commission Payment. During the Term, Serono shall pay to OSI ** the
amounts set forth in this Section 6.6 (each, a "Commission Payment"). The
Commission Payment is calculated based on a percentage of the Net Sales in each
Calendar Year during the Term, and the applicable percentage shall change upon
the occurrence of certain events and as Net Sales in the applicable Calendar
Year exceed certain increments as follows:

                (a) During each Calendar Year from the Effective Date  **:

<TABLE>
<CAPTION>
                Increments of Aggregate Annual           Commission
                         Net Sales                      Applicable to
                 (in Millions of US Dollars)            Such Increment
                <S>                                     <C>
                         **                                **
                         **                                **
</TABLE>

                (b) during each Calendar Year from the ** to the **, ** of Net
Sales; and

                (c) during each Calendar Year following the **, ** of Net Sales.

        **. The Commission Payment owed to OSI for the last Calendar Quarter in
any Calendar Year during the Term shall equal the product of the cumulative Net
Sales for such Calendar Year and the applicable commission percentages set forth
above, minus the cumulative


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -34-
<PAGE>

amount of Commission Payments paid with respect to the prior Calendar Quarters
of such Calendar Year. Serono shall promptly notify OSI of the occurrence of the
**.

        6.7. Payment Currency. All amounts due under this Agreement shall be
paid to the designated party in United States dollars.

        6.8. Payments. All payments under this Agreement shall be made on or
before the date due and payable by electronic transfer in immediately available
funds to the respective account designated in writing by the applicable party at
least two (2) Business Days before the payment is due, but a party shall not be
required to provide any such notice unless such account has been changed since
such notice was last provided. OSI shall notify Serono's treasurer, or such
other party as Serono's treasurer shall designate in writing, by facsimile
transmission as to the date and amount of any payment that OSI shall make prior
to such transfer. Serono shall notify OSI's treasurer, or such other party as
OSI's treasurer shall designate in writing, by facsimile transmission as to the
date and amount of any payment that Serono shall make prior to such transfer.
All payments under this Agreement shall bear interest from the date due and
payable until paid at an annual rate equal to **.

        6.9. Taxes. Unless otherwise required by law, each party shall be
responsible for paying and reporting all of its own taxes (including VAT or
withholding taxes) and fees incurred in connection with this Agreement.

        6.10. Withholding Taxes. Notwithstanding Section 6.9 each party shall be
indemnified against and held harmless by the other party (or its assignee) from
any incremental tax liability (including VAT or withholding taxes) imposed on
such party as the result of an assignment by the other party of its rights or
obligations under this Agreement pursuant to Section 14.5. In the event of any
such assignment, (i) the assignee shall gross up any payments it makes to the
extent


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -35-
<PAGE>

necessary so that the net payment received by the non-assigning party after any
such incremental tax liability equals the amount due under this Agreement; and
(ii) for the avoidance of doubt, the non-assigning party shall not be required
to pay any gross up or other amounts to the assigning party on account of any
taxes (including VAT or withholding taxes) that would not have been imposed but
for such assignment.

                                   ARTICLE VII
                             ACCOUNTING AND REPORTS

        7.1. Books and Records. Serono shall keep and shall cause to be kept
accurate records in sufficient detail to enable the Commission Payments
described in Section 6.6 to be determined and to be verified by OSI.

        7.2. Audit. Upon the written request of OSI, at OSI's expense and not
more than once in any Calendar Year, Serono shall permit an independent
accountant of national prominence selected by OSI, and approved by Serono (which
approval shall not be unreasonably withheld), to have access during normal
business hours to those records of Serono or its Affiliates as may be reasonably
necessary to verify the accuracy of the reports furnished by Serono pursuant to
Section 6.4, in respect of any Calendar Quarter ending not more than two (2)
years prior to the date of such notice. Such accountant shall not disclose any
information except that which should properly be contained in a report required
under Section 6.4 of this Agreement. Upon the expiration of two (2) years
following the end of any Calendar Quarter, the calculation of amounts payable
with respect to such Calendar Quarter shall be binding and conclusive upon OSI,
and Serono and its Affiliates shall be released from any liability or
accountability with respect to payments for such Calendar Quarter. The report
prepared by such independent accountant, a copy of which shall be sent or
otherwise provided to Serono by such independent accountant at the same time it
is sent or otherwise provided to OSI, shall contain the conclusions of such
independent accountant regarding the audit and will specify that the amounts
paid to OSI


                                      -36-
<PAGE>

for the period under audit were correct or, if incorrect, the amount of any
underpayment or overpayment. If such independent accountant's report shows any
underpayment, Serono shall remit or shall cause its Affiliates to remit to OSI
within thirty (30) days after Serono's receipt of such report, (i) the amount of
such underpayment with interest as set forth in Section 6.8, and (ii) if such
underpayment exceeds ** of the total amount owed for the period then being
audited, the reasonable and necessary fees and expenses of such independent
accountant performing the audit, subject to reasonable substantiation thereof.
Any overpayments shall be fully creditable against amounts payable in subsequent
payment periods or remitted to Serono, at Serono's request. OSI agrees that all
information subject to review under this Section 7.2 shall be deemed
Confidential Information of Serono and that OSI shall retain and cause its
accountant to retain all such information in confidence in accordance with
Article IX hereof.

        7.3. Sales Force Efforts. In addition to those records that OSI is
required to maintain pursuant to Section 2.11 or Law, for two (2) years
following each Calendar Year, OSI shall keep records relating to the Promotion
and Detailing activities reported in the Activities Reports for such Calendar
Year. Upon reasonable prior written notice to OSI, such records shall be
available for inspection and audit by Serono once per year to determine
compliance with the terms of this Agreement.

                                  ARTICLE VIII
                          INTELLECTUAL PROPERTY RIGHTS

        8.1. Trademark and Corporate Logos.

                8.1.1 Promotion. The Product shall be promoted and sold solely
under the Trademark and shall be packaged and labeled with Serono's trade dress,
Serono's corporate logo, and OSI's corporate logo. As soon as is reasonably
practical after the Effective Date,


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -37-
<PAGE>

Serono shall design the packaging and labeling for the Product. OSI shall
reimburse Serono for all costs incurred by Serono in connection with modifying
the existing packaging and labeling for the Product to incorporate OSI's logo.
The Product will be packaged using the redesigned packaging and labeling only
after the stock of packaging and labeling materials in existence or production
on the Effective Date is exhausted, unless OSI agrees to pay for the replacement
of such unused stock of packaging and labeling materials. Serono agrees to
promptly provide to OSI upon reasonable request an estimated cost for the
replacement of the then-current stock of packaging and labeling materials. Any
amounts payable by OSI pursuant to this Section 8.1.1 shall be invoiced to OSI
and payable within thirty (30) days of the date of such invoice. All training
materials utilized by OSI hereunder and Promotional Materials shall bear the OSI
corporate logo and the Serono corporate logo. Serono shall provide to OSI an
electronic copy of Serono's corporate logo for use on the Promotional Materials
and the training materials. OSI shall provide to Serono an electronic copy of
OSI's corporate logo for use on the Product. During the Term, Serono grants to
OSI the non-exclusive right to use the Serono corporate logo in the Territory
solely for the purpose of OSI's Promotion and Detailing of the Product in
accordance with the terms of this Agreement. During the Term and for a
reasonable period of time thereafter as described below, OSI grants to Serono
the non-exclusive right to use the OSI corporate logo in the Territory solely
for the purpose of Serono's promotion of the Product. Except as contemplated
herein, neither party shall otherwise have any rights in or to the other party's
trademarks or corporate logo or the goodwill pertaining thereto. OSI agrees that
upon termination or expiration of this Agreement it will discontinue forthwith
all use of the Trademark and the Serono corporate logo. Serono agrees that
following the termination or expiration of the Agreement, it will promptly
discontinue all use of the OSI corporate logo; provided, however, that Serono
shall be permitted to use all Promotional Materials and training materials and
to sell all Product inventory in existence or in production at the time of such
termination or expiration.


                                      -38-
<PAGE>

                8.1.2 Infringement. OSI shall inform Serono promptly of any
infringement of or challenge to the Trademark in the Territory, in each case
whether actual or threatened, which comes to the notice of OSI. As between OSI
and Serono, Serono shall have the exclusive right, at its sole cost and expense,
to take action in respect of the registration, defense, infringement and
maintenance of the Trademark, and OSI shall provide reasonable assistance and
cooperation with such activities as Serono may reasonably request, at Serono's
sole cost and expense.

        8.2. Copyrights. Subject to Sections 2.7 and 2.10, Serono shall own all
copyrights relating to the Promotional Materials and to the training materials
for the Sales Representatives and the Medical Science Liaisons, and such
copyrights shall be deemed Copyrights. As between OSI and Serono, Serono shall
have the exclusive right, at its sole cost and expense, to take action in
respect of the registration, defense, and infringement of the Copyrights, and
OSI shall provide reasonable assistance and cooperation with such activities as
Serono may reasonably request, at Serono's sole cost and expense.

        8.3. Know-How. All commercial information relating to the Product in the
Field which is not known to the public and is developed during the Term, by or
on behalf of either party acting alone or jointly, in connection with the
co-promotion or other activities contemplated under this Agreement shall be
owned by Serono and shall be deemed Know-How; provided, however, that Know-How
shall not include any data or information that compose the regulatory approvals
relating to the Product, including the NDA, or any data, results or other
information relating to the Product and arising from the Clinical Trials. Serono
shall have the exclusive right, at its sole cost and expense, to take action in
respect of the maintenance, protection, defense, and infringement of the
Know-How, including by filing any patent applications with respect thereto, and
OSI shall provide reasonable assistance and cooperation with such activities as
Serono may reasonably request, at Serono's sole cost and expense.


                                      -39-
<PAGE>

        8.4. Patent. OSI will not make any admission or take any action that
would reasonably be expected (such expectation to be as of the time such
admission is made or such action is taken) to (i) render a Valid Claim under the
Patent invalid or unenforceable, or (ii) materially limit Serono's or the Patent
owner's ability to prosecute, defend or enforce the Patent. OSI shall inform
Serono promptly of any infringement of or challenge to the Patent in the
Territory, in each case whether actual or threatened, which comes to the notice
of OSI. As between OSI and Serono, Serono shall have the exclusive right, at its
sole cost and expense, to take action in respect of the prosecution,
maintenance, defense and enforcement of the Patent, and OSI shall provide
reasonable assistance and cooperation with such activities as Serono may
reasonably request, at Serono's sole cost and expense.

        8.5. License Agreement and Manufacturing Agreement. Serono covenants and
agrees with OSI that Serono: (i) shall not execute, or otherwise permit to be
made, any amendment, modification or waiver to the License Agreement or
Manufacturing Agreement that would have a material adverse effect on OSI's
Promotion and Detailing of the Product, without the prior written consent of
OSI; (ii) shall not terminate the License Agreement, without the prior written
consent of OSI; and (iii) shall not take any action that might reasonably be
expected to result in the termination of the License Agreement or the
Manufacturing Agreement by the counterparties thereto.

                                   ARTICLE IX
                            CONFIDENTIAL INFORMATION

        9.1. Treatment of Confidential Information. During the Term and for
seven (7) years after the expiration or termination of this Agreement, each
party shall maintain Confidential Information of the other party in confidence,
and shall not disclose, divulge or otherwise communicate such Confidential
Information to third parties or use it for any purpose other than performance of
this Agreement.


                                      -40-
<PAGE>

        9.2. Disclosure to Affiliates and Agents. Each party may disclose
Confidential Information to its Affiliates and its and their officers,
directors, employees, consultants and agents, and Serono may disclose
Confidential Information to the counterparties to the Manufacturing Agreement
and the License Agreement, in connection with performance of this Agreement, but
only to the extent necessary to enable such parties to perform their obligations
hereunder or under the applicable agreement, as the case may be; provided that
such officers, directors, employees, consultants, and agents have entered into
appropriate confidentiality agreements for secrecy and non-use of such
Confidential Information containing provisions no less onerous than those set
forth herein.

        9.3. Injunctive Relief. Each party acknowledges and agrees that the
provisions of this Article IX are reasonable and necessary to protect the other
party's interests in its Confidential Information, that any breach of the
provisions of this Article IX may result in irreparable harm to such other
party, and that the remedy at law for such breach may be inadequate.
Accordingly, in the event of any breach or threatened breach of the provisions
of this Article IX by a party hereto, the other party, in addition to any other
relief available to it at law in equity or otherwise, shall be entitled to seek
temporary and permanent injunctive relief restraining the breaching party from
engaging in and/or continuing any conduct that would constitute a breach of this
Article IX, without the necessity of proving actual damages or posting a bond or
other security.

                                    ARTICLE X
                 REPRESENTATIONS, WARRANTIES AND INDEMNIFICATION

        10.1. Serono's Representations. Serono hereby represents and warrants as
of the Effective Date as follows:

                (a) Serono has the corporate power and authority to execute and
deliver this Agreement and to perform its obligations hereunder, and the
execution, delivery and


                                      -41-
<PAGE>

performance of this Agreement have been duly and validly authorized and approved
by proper corporate action on the part of Serono.

                (b) Neither the execution and delivery of this Agreement nor the
performance hereof by Serono requires Serono to obtain any permits,
authorizations or consents from any Governmental Authority or from any other
party (including Immunex Corporation with respect to the License Agreement); and
such execution, delivery and performance will not result in the breach of or
give rise to any termination of any agreement to which Serono may be a party and
which relates to the Product, including the License Agreement and the
Manufacturing Agreement.

                (c) There are no actions (including class actions), suits,
proceedings or claims pending or, to the knowledge of Serono, threatened against
Serono or any of its Affiliates at law or in equity or before or by any
Governmental Authority in the Territory, relating to the Product.

                (d) Serono has not received written notice of any orders,
investigations, actions or proceedings, or of any alleged violations or
noncompliance with the NDA, or any warning letters, in each such case, that
would reasonably be expected to result in the revocation, suspension or material
adverse modification of the NDA or otherwise would reasonably be expected to
have a material adverse effect on (i) OSI's ability to Promote and Detail the
Product or (ii) Net Sales.

                (e) Other than **, there are no agreements that have been
assumed or entered into by Serono and are currently in effect that offer a
discount on the purchase price of the Product; provided, however, that such
representation and warranty shall not be deemed to extend to any agreements or
other arrangements with respect to discounts on the purchase price


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -42-
<PAGE>

of the Product that are entered into with any Governmental Authorities or
offered through programs (such as Medicare and Medicaid) administered by any
Governmental Authorities.

                (f) The License Agreement and the Manufacturing Agreement, in
the form provided by Serono to OSI, are in full force and effect and have not be
modified or amended and there exists no default under either agreement by
Serono, or to Serono's knowledge, any other party to either agreement or any
event which, with the notice or lapse of time or both, would constitute a
default thereunder by Serono or, to Serono's knowledge, any other party to
either such agreement.

                (g) Serono has not intentionally withheld from OSI any material
information in Serono's possession with respect to the safety and effectiveness
of the Product.

                (h) With respect to the redacted version of the License
Agreement provided by Serono to OSI, the redacted portions of the License
Agreement, whether taken alone or together with unredacted provisions of the
License Agreement, (i) do not impose any additional obligations on OSI and (ii)
do not in any way conflict with any provision of this Agreement.

                (i) Serono is not currently using any devices for dispensing or
administering the Product that accompany the Product as it is sold.

                (j) **

        10.2. OSI's Representations. OSI hereby represents and warrants as of
the Effective Date as follows:


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -43-
<PAGE>

                (a) OSI has the corporate power and authority to execute and
deliver this Agreement and to perform its obligations hereunder, and the
execution, delivery and performance of this Agreement have been duly and validly
authorized and approved by proper corporate action on the part of OSI.

                (b) Neither the execution and delivery of this Agreement nor the
performance hereof by OSI requires OSI to obtain any permits, authorizations or
consents from any Governmental Authority or from any other person; and such
execution, delivery and performance will not result in the breach of or give
rise to any termination of any agreement or contract to which OSI may be a
party, which termination would reasonably be expected to have a material adverse
effect on OSI's ability to perform hereunder.

        10.3. Indemnification of OSI.

                10.3.1 Indemnity. Serono shall indemnify, defend and hold OSI
and its Affiliates and its and their respective directors, officers, employees
and agents (the "OSI Parties") harmless from and against any and all Losses
incurred, suffered or sustained by the OSI Parties, or to which the OSI Parties
become subject, to the extent arising out of any third party claims, actions,
suits, or proceedings ("Third Party Claims") resulting from or relating to **
(iv) the breach by Serono of any of its representations, warranties or covenants
herein; or (v) any gross negligence, bad faith, recklessness or willful
misconduct of any of the Serono Parties.

                10.3.2 Limitation. None of the obligations in Section 10.3.1
shall apply to the extent that any Loss results from any breach of this
Agreement by OSI or any gross negligence, bad faith, recklessness, or willful
misconduct of any of the OSI Parties.

        10.4. Indemnification of Serono.


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -44-
<PAGE>

                10.4.1 Indemnity. OSI shall indemnify, defend and hold Serono
and its Affiliates and its and their respective directors, officers, employees
and agents and the counterparties to the Manufacturing Agreement and the License
Agreement (the "Serono Parties") harmless from and against any and all Losses
incurred, suffered or sustained by the Serono Parties, or to which the Serono
Parties become subject, resulting from or relating to ** (ii) the breach by OSI
of any of its representations, warranties or covenants herein; or (iii) or any
gross negligence, bad faith, recklessness, or willful misconduct of any of the
OSI Parties.

                10.4.2 Limitation. None of the indemnities in Section 10.4.1
shall apply to the extent that any Loss results from any breach of this
Agreement by Serono or any gross negligence, bad faith, recklessness, or willful
misconduct of the Serono Parties.

        10.5. Indemnification Procedures for Third Party Claims. The following
procedures shall apply to any Third Party Claim for which an OSI Party or a
Serono Party, as the case may be (the "Indemnified Party"), may be entitled to
indemnification under this Article X. To be eligible to be indemnified for a
Third Party Claim, the Indemnified Party shall (i) provide the party required to
indemnify the Indemnified Party (the "Indemnifying Party") with prompt written
notice of the Third Party Claim giving rise to the indemnification obligation
under this Article X, which notice shall include a reasonable identification of
the alleged facts giving rise to such Third Party Claim; provided, however, that
the failure to provide prompt notice shall not relieve the Indemnifying Party of
any of its obligations under this Article X except to the extent the
Indemnifying Party is actually prejudiced thereby; (ii) provide the Indemnifying
Party with the exclusive ability to defend (with the reasonable cooperation of
the Indemnified Party) against the Third Party Claim; and (iii) not settle,
admit (unless legally required to do so) or materially prejudice the Third Party
Claim without the Indemnifying Party's prior written consent. The Indemnified
Party shall reasonably cooperate with the Indemnifying Party, at the
Indemnifying Party's expense, in the defense of any Third Party Claim.
Notwithstanding the foregoing, the Indemnified Party shall have the right to
participate and have counsel selected by it participate, at

----------------
**This portion has been redacted pursuant to a confidential treatment request.

                                      -45-
<PAGE>

the Indemnified Party's expense, in any action for which the Indemnified Party
seeks to be indemnified by the Indemnifying Party. The Indemnifying Party shall
not settle or compromise, or consent to the entry of any judgment with respect
to, any Third Party Claim, without the prior written consent of the Indemnified
Party, which will not be unreasonably withheld or delayed; provided, however,
that the Indemnifying Party may settle or compromise any Third Party Claim if
the settlement or compromise provides for an unconditional release of the
Indemnified Party.

        10.6. Non-Duplicative Payment. In calculating amounts payable to an
Indemnified Party, the amount of the Losses shall not be duplicative of any
other Losses for which an indemnification claim has been made and shall be
computed net of (i) payments recoverable by the Indemnified Party under any
insurance policy with respect to such Losses; (ii) any prior or subsequent
recovery by the Indemnified Party from any third party with respect to such
Losses; or (iii) any tax benefit receivable by the Indemnified Party with
respect to such Losses.

        10.7. Insurance. Subject to generally available and customary terms and
conditions of general liability insurance policies, each party shall as soon as
practicable, but in no event later than sixty (60) days after the Effective
Date, obtain, maintain and keep in force for the Term comprehensive general
liability insurance, including coverage for products and completed operations,
covering its indemnification obligations hereunder with a minimum limit of **
combined single limit for Bodily Injury and Property Damage. It is understood
that such insurance shall not be construed to limit a party's liability with
respect to such indemnification obligations. Such insurance shall be placed with
a first class insurance carrier with at least a BBB rating by Standard & Poor's.
Promptly after execution and delivery of this Agreement, each party shall
furnish a certificate of insurance to the other party evidencing the foregoing
endorsements, coverage and limits, and providing that such insurance shall not
expire or be canceled or modified without at least thirty (30) days prior notice
to the other party.


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -46-
<PAGE>

        10.8. Limitation of Liability. IN NO EVENT SHALL OSI OR SERONO BE LIABLE
FOR SPECIAL, INDIRECT, INCIDENTAL, CONSEQUENTIAL, PUNITIVE OR EXEMPLARY DAMAGES
(INCLUDING LOSS OF REVENUE OR LOSS OF PROFITS) RESULTING FROM OR RELATED TO THIS
AGREEMENT, HOWEVER CAUSED AND UNDER ANY THEORY OF LIABILITY, EVEN IF SUCH PARTY
HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, **.

                                   ARTICLE XI
                              TERM AND TERMINATION

        11.1. Term. This Agreement shall be effective as of the Effective Date
and shall continue in force until the expiration of the Term.

        11.2. Termination for Breach. Either party (the "Non-breaching Party")
may terminate this Agreement by written notice to the other party (the
"Breaching Party") if the Breaching Party is in default of any of its material
obligations hereunder and fails to remedy such default within ninety (90) days
(thirty (30) days in the case of a payment default) after written notice thereof
by the Non-breaching Party specifying in reasonable detail the nature of such
breach.

        11.3. Termination Upon Other Events. In the event that during the
Maintenance Term (i) the NDA (as it may be modified from time to time) is
revoked by the FDA or (ii) the License Agreement is terminated, OSI may
terminate immediately this Agreement. Within **, OSI may terminate this
Agreement with ** prior written notice to Serono if Net Sales ** during the
immediately preceding Calendar Year.

        11.4. Termination after the First Generic Date. OSI may terminate this
Agreement with ninety (90) days prior written notice to Serono at any time after
the First Generic Date.


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -47-
<PAGE>

        11.5. Termination for Bankruptcy. This Agreement may be immediately
terminated by either party if the other party becomes insolvent, makes an
assignment for the benefit of creditors, is the subject of proceedings in
voluntary or involuntary bankruptcy instituted on behalf of or against such
party, or has a receiver or trustee appointed for all or substantially all of
its property, provided, however, that in the case of an involuntary bankruptcy
proceeding such right to terminate shall only become effective if the party
consents to the involuntary bankruptcy or such proceeding is not dismissed
within ninety (90) days after the filing thereof.

        11.6. Survival of Obligations. Notwithstanding any termination or
expiration of this Agreement, (i) neither party shall be relieved of any
obligations incurred prior to such termination or expiration, (ii) the
obligations of the parties with respect to the protection and nondisclosure of
Confidential Information (Article IX), Indemnification (Article X), as well as
any other Section of this Agreement which is required to give effect to such
termination or expiration or the consequences of such termination or expiration,
shall survive such termination or expiration, and (iii) unless this Agreement
expressly provides that termination shall be the sole and exclusive remedy for a
particular breach hereof, either party's right to terminate this Agreement shall
be in addition to and not in lieu of all other rights or remedies that the party
giving notice of termination may have at law, in equity or otherwise. If this
Agreement is terminated as a result of the termination of the License Agreement,
then this Agreement at the option of the counterparty to the License Agreement
shall be assigned by Serono to such counterparty. Upon termination or expiration
of this Agreement, each party shall within thirty (30) days thereafter destroy
all Confidential Information of the other party in its possession and/or under
its control; provided, however, that each party shall have the right to retain
one archival copy of Confidential Information for its legal files for the sole
purposes of establishing its rights and determining its obligations under this
Agreement. At the request of the other party, a party shall deliver a
certification, executed by an officer of such party, that all Confidential


                                      -48-
<PAGE>

Information of the other party has been destroyed as set forth in this Section
11.6, subject to the right to retain one archival copy as set forth in this
Section 11.6.

                                   ARTICLE XII
                                 NON-COMPETITION

        12.1. **. During the Maintenance Term or until the earlier termination
of this Agreement, without Serono's prior written approval, OSI shall not,
directly or indirectly, develop, manufacture, market, sell, detail, promote or
distribute **. Following the ** until the end of the Term, Serono shall have the
right to terminate this Agreement in the event OSI, directly or indirectly,
develops, manufactures, markets, sells, details, promotes or distributes **.

        12.2. **. During the Maintenance Term or until the earlier termination
of this Agreement, without Serono's prior written approval, OSI shall not,
directly or indirectly, develop, manufacture, market, sell, detail, promote or
distribute **. For the avoidance of doubt, the limitations on OSI set forth in
this Section 12.2 are in addition to, rather than in lieu of, those set forth in
Section 12.1.

                                  ARTICLE XIII
                               DISPUTE RESOLUTION

        13.1. Disputes Concerning Matters Subject to Determination by the JMC.
The parties intend that, to the maximum extent practicable, that with respect to
matters subject to determination by the JMC, they shall reach decisions
hereunder cooperatively through the deliberations of the JMC and by consent of
its members as described in Section 3.3. In situations in which such cooperative
decision making does not occur, any two members of the JMC may institute the
procedure described in this Article XIII. In such circumstances, a summary of
the


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -49-
<PAGE>

proposed JMC action and the unresolved dispute will be provided in writing to
the CEO of OSI and the CEO of Serono's Affiliate, Serono, S.A. The parties'
CEO's or, at their election, an executive officer of each party who has direct
reporting responsibility to the CEO of that party shall discuss the proposed JMC
action, and shall meet and attempt to resolve the matter by either approving in
writing the proposed JMC action (whether or not in a revised form) or agreeing
in writing to reject it within five (5) Business Days following the receipt by
them of the summary of the proposed action and the unresolved dispute (or such
lesser or longer period as they may agree is a useful period for their
discussions). In the event that the parties' CEO's or their designees are unable
pursuant to the preceding sentence to resolve any dispute **.

        13.2. Other Disputes. Notwithstanding the foregoing, any dispute
concerning any matter that is not specifically described herein as subject to
determination by the JMC, including a dispute asserting breach of this
Agreement, shall be submitted exclusively to the federal court in the State of
Delaware, and the parties hereby consent to the jurisdiction and venue of such
court.

                                   ARTICLE XIV
                                  MISCELLANEOUS

        14.1. Entire Agreement. This Agreement, together with all of the
Exhibits hereto, constitutes the entire agreement between the parties and
supersedes all prior and contemporaneous oral and written agreements,
understandings or arrangements relating to the subject matter hereof.

        14.2. Governing Law. This Agreement shall be governed by and construed
in accordance with the laws of the State of Delaware, without giving effect to
the doctrine of conflict of laws.


----------
** This portion has been redacted pursuant to a confidential treatment request.


                                      -50-
<PAGE>

        14.3. Notices. All notices, reports and other communications by OSI or
Serono to the other party shall: (i) be in writing; (ii) refer specifically to
this Agreement; and (iii) be sent by electronic or facsimile transmission for
which a confirmation of delivery is obtained or by express courier services
providing evidence of delivery, in each case to the respective address specified
below (or to such updated address as may be specified in writing to the other
party from time to time).

                If to Serono:

                      Ares Trading S.A.
                      Chateau de Vaumarcus
                      2028 Vaumarcus
                      Switzerland
                      Attn: General Manager
                      Fax: 41-32-836-3899

                with a copy to:

                      Serono International S.A.
                      15 bis, Chemin des Mines
                      Case Postale 54
                      CH-1211 Geneve 20
                      Switzerland
                      Attn: General Counsel
                      Fax: 41-22-739-3070

                and a copy to:

                      Serono, Inc.
                      One Technology Place
                      Rockland, Massachusetts 02370
                      Attn: Vice President and General Counsel, North America
                      Fax: 781-681-2934

                If to OSI:

                      OSI Pharmaceuticals, Inc.
                      58 South Service Road
                      Melville, New York  11747
                      Attn:  Geoffrey Cooper, Ph.D.
                      Vice President, Corporate Development


                                      -51-
<PAGE>

                      Fax: (631) 962-2021

                with a copy to:

                      OSI Pharmaceuticals, Inc.
                      58 South Service Road
                      Melville, New York  11747
                      Attn:  Barbara A. Wood, Esq.
                      General Counsel
                      Fax: (631)293-2218

                and a copy to:

                      Mintz Levin Cohn Ferris Glovsky and Popeo, P.C.
                      666 Third Avenue, 24th Floor
                      The Chrysler Center
                      New York, New York  10017
                      Attn: Joel I. Papernik, Esq.
                      Fax: (212) 983-3115

Such notice, report or other communication will be deemed effective as of the
date so delivered either by courier service or by electronic or facsimile
transmission.

        14.4. Force Majeure. Neither party shall be in breach of this Agreement
if there is any failure of performance under this Agreement (except for payment
of any amounts due hereunder) occasioned by any act of God, fire, act of
government or state, war, civil commotion, insurrection, terrorism, failure or
delay of transportation, embargo, prevention from or hindrance in obtaining
energy or other utilities, labor disputes of whatever nature or any other reason
beyond the control and without the fault or negligence of the party affected
thereby (a "Force Majeure Event"). Such excuse shall continue as long as the
Force Majeure Event continues. Upon cessation of such Force Majeure Event, the
affected party shall promptly resume performance hereunder. Each party agrees to
give the other party prompt written notice of the occurrence of any Force
Majeure Event, the nature thereof, and the extent to which the affected party
will be unable fully to perform its obligations hereunder. The affected party
further agrees


                                      -52-
<PAGE>

to use reasonable efforts to correct the Force Majeure Event as quickly as
possible and to give the other party prompt written notice when it is again
fully able to perform such obligations.

        14.5. Assignment. Except as otherwise provided herein, neither this
Agreement nor any of the rights or obligations hereunder may be assigned by
either party without the prior consent of OSI, in the case of any assignment by
Serono, or Serono, in the case of any assignment by OSI, except assignment, in
whole or in part, to an Affiliate of the assigning party or to any other party
who acquires all or substantially all of the business of the assigning party by
merger, sale of assets or otherwise, so long as such Affiliate or other party
agrees in writing to be bound by the terms of this Agreement. To the extent any
rights or obligations of a party are assigned to an Affiliate of such party then
any business transaction, change in control or other event that, in each case,
causes such Affiliate to cease to be an Affiliate of the assigning party, shall
be deemed an assignment of the rights or obligations held by such former
Affiliate and shall require prior written consent of the other party. Any
attempted assignment in violation hereof shall be null and void.

        14.6. Performance by an Affiliate. Each of Serono and OSI acknowledge
that obligations under this Agreement may be performed by Affiliates of Serono
and OSI. Each of Serono and OSI guarantee performance of this Agreement by its
Affiliates, notwithstanding any assignment to Affiliates in accordance with
Section 14.5 of this Agreement.

        14.7. Amendments and Waivers. No terms or provisions of this Agreement
shall be varied or modified by any prior or subsequent statement, conduct or act
of either of the parties, whether oral or written, except that the parties may
amend this Agreement by written instruments specifically referring to, and
executed in the same manner as, this Agreement. No waiver of any right or remedy
hereunder shall be effective unless in a writing signed by the party to be
bound, nor shall any waiver in one instance constitute a waiver of the same or
any other right or remedy in any other instance. No delay or omission by a party
to exercise or avail itself of any right,


                                      -53-
<PAGE>

power or privilege that it has or may have hereunder shall operate as a waiver
of any right, power or privilege by such party.

        14.8. Severability. If any provision hereof should be held invalid,
illegal or unenforceable in any respect in any jurisdiction, then, to the
fullest extent permitted by law: (i) all other provisions hereof shall remain in
full force and effect in such jurisdiction and shall be liberally construed in
order to carry out the intentions of the parties hereto as nearly as is
possible; and (ii) such invalidity, illegality or unenforceability shall not
affect the validity, legality or enforceability of such provision in any other
jurisdiction. If the terms and conditions of this Agreement are materially
altered as a result of this Section 14.8, the parties shall attempt to
renegotiate the terms and conditions of this Agreement, in good faith, to
resolve any inequities.

        14.9. Counterparts. This Agreement may be executed in counterparts, each
of which shall be deemed an original, and all of such counterparts taken
together shall constitute one and the same instrument.

        14.10. Relationship of the Parties. Each party shall bear its own costs
incurred in the performance of its obligations hereunder without charge or
expense to the other except as expressly provided in this Agreement. No employee
or representative of a party shall have any authority to bind or obligate the
other party to this Agreement for any sum or in any manner whatsoever, or to
create or impose any contractual or other liability on the other party without
such party's prior written approval. For all purposes, and notwithstanding any
other provision of this Agreement to the contrary, nothing in this Agreement
shall be construed to establish a relationship of partners or joint venturers
between the parties.

        14.11. Non-Solicitation of Employees. During the Term, neither party
shall, directly or indirectly, recruit, or solicit any employee of the other
party or any of such other party's


                                      -54-
<PAGE>

Affiliates if such employee has been materially involved in the performance of
this Agreement, except pursuant to general solicitations not targeted at such
employees.

        14.12. Press Releases. The parties hereby each approve the form of joint
press release set forth in Exhibit D hereto, and will cooperate in the release
thereof as soon as practicable after the signature of this Agreement by the
parties. No other public announcement or other disclosure to third parties
concerning the existence or terms of this Agreement shall be made, either
directly or indirectly, by either party hereto, without first obtaining the
written approval of the other party, which shall include agreement upon the
nature and text of such announcement or disclosure; provided, however, that
Serono shall be permitted to disclose the terms of this Agreement to the
counterparty to the License Agreement. The party desiring to make any such
public announcement or other disclosure shall inform the other party of the
proposed announcement or disclosure by providing the other party with a written
copy thereof, and allowing reasonably sufficient time prior to public release to
permit such other party to comment upon such announcement or disclosure. Once
any such public announcement or disclosure has been approved in accordance with
this Section 14.12, which approval shall not be unreasonably withheld, then
either party may appropriately communicate information contained in such
permitted announcement or disclosure. Notwithstanding the foregoing, a party may
make such disclosure where required by applicable Law or applicable stock
exchange regulation or order or other ruling of a competent court, provided,
however, that the disclosing party shall use reasonable efforts to notify the
other party prior to making such disclosure. Each party agrees that it shall
reasonably cooperate with the other with respect to all disclosures regarding
this Agreement to the Securities and Exchange Commission and any other
governmental or regulatory agencies, including requests for confidential
treatment of proprietary information of either party included in any such
disclosure.

        14.13. Third Party Beneficiaries. None of the provisions of this
Agreement shall be for the benefit of or enforceable by any third party,
including any creditor of either party hereto. No


                                      -55-
<PAGE>

such third party shall obtain any right under any provision of this Agreement or
shall by reason of any such provision make any claim in respect of any debt,
liability or obligation (or otherwise) against either party hereto.

        14.14. Headings. The article and section headings contained herein are
for reference only and shall not be considered a part of this Agreement, nor
shall they in any way affect the interpretation hereof.

        14.15. Interpretation. 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.

        14.16. Further Assurances; Covenant to Cooperate. Each of the parties
agree, during the Term, that it will execute and deliver any and all such
documents and instruments and take any and all such other actions as the other
party may reasonably request in order to consummate and make effective the
transactions contemplated by this Agreement.

        14.17. No Set Off. No party shall have any right to set-off any amount
owed by it to the other party or an Affiliate thereof under this Agreement from
any amount owed by such other party or one of its Affiliates to the first party
under this Agreement, another agreement or otherwise, without the prior written
consent of the other party.


                                      -56-
<PAGE>

        IN WITNESS WHEREOF, the parties have executed and delivered this
Agreement to be effective as of the Effective Date.

ARES TRADING S.A.                           OSI PHARMACEUTICALS, INC.
By:   /s/ Leon Bushara                      By:   /s/ Colin Goddard, Ph.D.
   ---------------------------------           ---------------------------------
Name:     Leon Bushara                      Name:     Colin Goddard, Ph.D.
     --------------------------------            -------------------------------
Title:    Authorized Representative         Title:    Chief Executive Officer
      -------------------------------              -----------------------------


                                      -57-
<PAGE>

                                    EXHIBIT A

                             ONGOING CLINICAL TRIALS

                                       **

----------
** This portion has been redacted pursuant to a confidential treatment request.



                                      A-1
<PAGE>

                                    EXHIBIT B

                   ADVERSE EVENT REPORTING; PRODUCT COMPLAINTS

This is to advise the parties of the requirements for data exchange between them
regarding reports of adverse experiences and product complaints related to the
use of the Product which will be marketed in accordance with this Agreement.

It is a requirement of the FDA that the parties record, investigate, summarize
and review all adverse experiences and product complaints associated with the
Product. The parties understand that reporting requirements differ from country
to country, and because at least one party is a multinational company often
subject to multiple jurisdictions, the reporting standards contained herein may
be more stringent than FDA requirements. The parties require compliance with the
higher standard contained herein. The parties agree to adhere to requirements of
local laws and regulations, which relate to the reporting and investigation of
adverse experiences and product complaints.

In order to ensure that all relevant safety data related to the Product will be
duly reported to appropriate regulatory authorities, the parties agree to
establish within sixty (60) days after the effective date a detailed
Pharmacovigilance Agreement, outlining the responsibilities of each party in
connection with collecting and reporting of adverse events and product
complaints in accordance with the following provisions:

(i) All Product complaints and reports of adverse experiences associated with
the use of the Product shall be promptly transmitted by OSI to Serono. OSI shall
provide Serono all necessary assistance to follow up and document such Product
complaints and reports of adverse experiences associated with the use of the
Product.

(ii) Serono shall promptly investigate all Product complaints and reports of
adverse experiences, associated with the use of the Product, upon receiving such
complaints or reports of adverse experiences associated with the use of the
Product.

(iii) Serono shall establish and maintain the global safety database for the
Product.


                                      B-1
<PAGE>

(iv) Serono shall submit reports of all adverse experiences associated with the
use of the Product and other required safety information, e.g., Field Alert
Reports, Periodic Safety Update Reports and Annual Safety Reports, to the FDA
and other Governmental Authorities, in accordance with the applicable legal
requirements, copies of which shall be promptly provided to OSI.

(v) Serono shall have the sole responsibility for revising the Product labeling,
as needed, to adequately warn of the potential risks identified by reports of
adverse drug experiences associated with the use of the Product and from Product
complaints, and shall notify OSI in writing of the approval of any such labeling
changes by the FDA or any other Governmental Authority.


                                      B-2
<PAGE>


                                    EXHIBIT C

                                       **

----------
** This portion has been redacted pursuant to a confidential treatment request.



                                      C-1
<PAGE>

                                    EXHIBIT D

                                  PRESS RELEASE


[(OSI) pharmaceutical LOGO]
                                                [serono LOGO]


                                                                    NEWS RELEASE

<TABLE>
<S>            <C>                                        <C>
Contact:       OSI Pharmaceuticals, Inc.                  Burns McClellan (representing OSI)
               Kathy Galante                              Jonathan Nuggent (investors)
               Director                                   Kathy Jones, Ph.D. (media)
               Investor & Public Relations                (212) 213-0006
               (631) 962-2000

               Serono in Geneva, Switzerland              Serono, Inc.,  Rockland, MA
               Media Relations: Tel: 41-22-739-36-00      Media Relations: Tel: 781-681-2340
               Fax:  41-22-739-30-85                      Fax: 781-681-2935
               http://www.serono.com                      http://www.seronousa.com
               Investor Relations: Tel: 41-22-739-36-01   Investor Relations: Tel: 781-681-2552
               Fax: 41-22-739-30-22                       Fax: 781-681-2912
               Reuters: SEOZ.VX/SRA.N
               Bloomberg: SEO VX/SRA US
</TABLE>


          SERONO AND OSI PHARMACEUTICALS ANNOUNCE AGREEMENT FOR OSI TO

                        MARKET NOVANTRONE(R) IN ONCOLOGY

MELVILLE, NEW YORK AND GENEVA, SWITZERLAND - MARCH 12, 2003 - OSI
Pharmaceuticals, Inc. (NASDAQ: OSIP) and Serono S.A. (virt-x: SEO and NYSE: SRA)
announced today that they have entered into an agreement by which OSI will
market and promote the drug Novantrone(R) (mitoxantrone concentrate for
injection) for the approved oncology indications in the United States. In
consideration for these exclusive rights, OSI will pay Serono initial fees
totaling $55 million plus maintenance fees in return for commissions on net
sales in oncology. To support Novantrone(R), OSI intends to build commercial
operations which will include a sales force and an associated marketing and
sales management infrastructure.

Novantrone(R) is approved by the U.S. Food and Drug Administration for the
treatment of acute nonlymphocytic leukemia (ANLL), which includes myelogenous,
promyelocytic, monocytic and


                                      D-1
<PAGE>

erythroid acute leukemias, and the relief of pain associated with advanced
hormone-refractory prostate cancer (HRPC). The drug is also approved for certain
advanced forms of multiple sclerosis (MS). Serono will continue to be
responsible for the marketing of the multiple sclerosis indication for
Novantrone(R) and book all U.S. sales in all indications. Total sales of
Novantrone(R) in 2002, were approximately $80 million. Serono acquired from
Amgen the U.S. rights to Novantrone(R) for both MS and oncology in December
2002.

"Gaining access to a high-quality, marketed oncology product to both build a
revenue base and allow us to seed a commercial organization has been a key
corporate goal over the last two years," stated Colin Goddard, Ph.D., Chief
Executive Officer of OSI Pharmaceuticals. "We see Novantrone(R) as a well
established therapeutic product in oncology of about the right size that became
available at the right time, and we have moved aggressively to secure this
opportunity. We believe our new relationship with Serono represents a win-win
for both parties. Further, we believe this deal, coupled with our recently
announced intention to acquire Cell Pathways' pro-apoptotic pipeline and the
marketed oncology-care product Gelclair(TM), represent major steps forward in
continuing to build a high quality oncology organization."

"We have found an excellent partner in OSI, who have a significant commitment to
developing a commercial presence in the field of oncology," said Ernesto
Bertarelli, Serono's Chief Executive Officer. "This agreement enables Serono to
focus on Novantrone(R) in our specialist area of multiple sclerosis, while
ensuring that the product continues to be well supported in its oncology
indications."

Novantrone(R) is a synthetic antineoplastic anthracenedione used intravenously
as an anti-cancer agent. The product was approved by the FDA in 1987 for ANLL
and in 1996 for the relief of pain associated with HRPC. It was registered for
MS indications in October 2000. It is a DNA-reactive agent that intercalates
into DNA through hydrogen bonding, causing crosslinks and strand breaks.
Novantrone(R) also interferes with RNA and is a potent inhibitor of
topoisomerase II, an enzyme responsible for uncoiling and repairing damaged DNA.

CONFERENCE CALL INFORMATION
OSI will host a conference call today, March 12th, at 10:00A.M. Eastern Time. To
access the live call or the seven-day archive via the Internet, log on to
www.osip.com. Please connect to OSI's website at least 15 minutes prior to the
conference call to ensure adequate time for any software download that may be
needed to view the webcast. Alternatively, please call 1-800-388-8975 (U.S.) or
1-973-694-2225 (international) to listen to the call. Telephone replay is
available approximately two hours after the call through March 19, 2003. To
access the replay, please call 1-800-428-6051(U.S.) or 1-973-709-2089
(international). The conference ID number is 287199.

ABOUT OSI
OSI Pharmaceuticals, Inc. is a leading biotechnology company focused on the
discovery, development and commercialization of high-quality, next-generation
oncology products that both extend and improve the quality-of-life for cancer
patients worldwide. OSI has a balanced pipeline of oncology drug candidates that
includes both next-generation cytotoxic agents and novel mechanism-based,
gene-targeted therapeutics. OSI's most advanced drug candidate,


                                      D-2
<PAGE>

Tarceva(TM) (erlotinib HCl), a small-molecule inhibitor of the EGFR gene, is
currently in Phase III clinical trials for lung and pancreatic cancers.

ABOUT SERONO
Serono is a global biotechnology leader. The Company has six recombinant
products on the market, Rebif(R), Gonal-F(R), Luveris(R),
Ovidrel(R)/Ovitrelle(R), Serostim(R) and Saizen(R) (Luveris(R) is not approved
in the USA). In addition to being the world leader in reproductive health,
Serono has strong market positions in neurology, metabolism and growth. Serono's
research programs are focused on growing these businesses and on establishing
new therapeutic areas. Currently, there are over 30 projects in development.

In 2002, Serono achieved worldwide revenues of US $1.546 billion, and a net
income of US $321 million, making it the third largest biotech company in the
world. Serono operates in 45 countries, and its products are sold in over 100
countries. Bearer shares of Serono S.A., the holding company, are traded on the
virt-x (SEO) and its American Depositary Shares are traded on the New York Stock
Exchange (SRA).

This news release contains forward-looking statements. These statements are
subject to known and unknown risks and uncertainties that may cause actual
future experience and results to differ materially from the statements made.
Factors that might cause such a difference include, among others, the impact of
acquisitions and divestitures on the synergies of OSI's programs, the success of
research and development activities and of pre-clinical development thereof, the
completion of clinical trials, the FDA review process and other governmental
regulation, pharmaceutical collaborators' ability to successfully develop and
commercialize drug candidates, competition from other pharmaceutical companies,
product pricing and third party reimbursement, and other factors described in
OSI Pharmaceuticals' filings with the Securities and Exchange Commission.

Some of the statements in this press release are forward looking. Such
statements are inherently subject to known and unknown risks, uncertainties and
other factors that may cause actual results, performance or achievements of
Serono S.A. and affiliates to be materially different from those expected or
anticipated in the forward-looking statements. Forward-looking statements are
based on Serono's current expectations and assumptions, which may be affected by
a number of factors, including those discussed in this press release and more
fully described in Serono's Annual Report on Form 20-F filed with the U.S.
Securities and Exchange Commission on May 21 2002. These factors include any
failure or delay in Serono's ability to develop new products, any failure to
receive anticipated regulatory approvals, any problems in commercializing
current products as a result of competition or other factors, our ability to
obtain reimbursement coverage for our products, and government regulations
limiting our ability to sell our products. Serono has no responsibility to
update the forward-looking statements contained in this press release to reflect
events or circumstances occurring after the date of this press release.

                                       ###

                                      D-3