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                                                                    Exhibit 10.4

                                                        April 21, 2005

                                     Amended and Restated May 31, 2005

Mr. Michael Atieh
10 Longwood Road
Morristown, NJ 07920

Re:  Amended and Restated Employment Agreement

Dear Mike:

      This letter is to confirm our understanding with respect to (i) your
future employment by OSI Pharmaceuticals, Inc. (the "Company"), (ii) your
agreement not to solicit employees or customers of the Company, or any present
or future parent, subsidiary or affiliate of the Company (each, a "Company
Affiliate" and collectively, together with the Company, the "Company", (iii)
your agreement to protect and preserve information and property which is
confidential and proprietary to the Company, and (iv) your agreement with
respect to the ownership of inventions, ideas, copyrights and patents which may
be used in the business of the Company (the terms and conditions agreed to in
this letter are hereinafter referred to as the "Agreement"). In consideration of
the mutual promises and covenants contained in this Agreement, and for other
good and valuable consideration, the receipt and sufficiency of which are hereby
mutually acknowledged, we have agreed as follows:

      1. Employment.

            (a) Subject to the terms and conditions of this Agreement, the
      Company will employ you, and you will be employed by the Company and/or
      any Company Affiliate designated by the Company, initially as Executive
      Vice President, Chief Financial Officer and Treasurer, of the Company
      reporting to the Chief Executive Officer (the "CEO") of the Company. You
      will have the responsibilities, duties and authority customarily
      performed, undertaken and exercised by a person in a similar executive
      capacity. You will also perform such other and/or different services for
      the Company as may be assigned to you from time to time by the CEO. The
      principal location at which you will perform such services will be the
      Company's headquarters located at 58 South

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      Service Road, Melville, New York, although you will be available to
      perform services at any other Company facility and to travel as the needs
      of business may require.

            (b) Devotion to Duties. While you are employed hereunder, you will,
      to the best of your ability, perform faithfully and diligently all duties
      assigned to you pursuant to this Agreement and will devote your full
      business time and energies to the business and affairs of the Company.
      While you are employed hereunder, you will not undertake any other
      employment from any person or entity without the prior written consent of
      the Company.

      2. Term. Except for earlier termination as provided for in Section 4
      hereof, your employment under this Agreement (the "Employment Term") shall
      be for an initial term commencing on May 31, 2005 (the "Effective Date")
      and ending on the third anniversary of the Effective Date (the "Initial
      Term"). Unless written notice is given of an intent not to extend the
      Initial Term or any extension thereof by you or the Company at least 90
      days prior to an anniversary of the Effective Date, the Employment Term
      shall be deemed, as of such 90th day, to have been extended and continue
      until the end of the successive 12-month period unless otherwise
      terminated as provided for in Section 4 hereof. In the event the Company
      elects not to renew the Employment Term, you shall be entitled to the
      payments and benefits set forth in Section 6(c).

      3. Compensation.

            (a) Base Salary. While you are employed hereunder, the Company will
      pay you a base salary at the annual rate of $410,000 (the "Base Salary").
      Your Base Salary will be reviewed on an annual basis each January (or such
      other time as determined by the CEO and/or the Compensation Committee of
      the Board of Directors of the Company (the "Board")), commencing with
      January, 2006. The Base Salary will be payable in equal installments in
      accordance with the Company's payroll practices as in effect from time to
      time. The Company will deduct from each such installment all amounts
      required to be deducted or withheld under applicable law or under any
      employee benefit plan in which you participate.

            (b) Bonus. In addition to the Base Salary, for each fiscal year of
      the Company ending during the Term of the Agreement, beginning with the
      2005 fiscal year, you will be eligible to receive a target bonus of
      between $200,000 - $300,000 , determined and payable in accordance with
      the Company's practices applicable to bonuses paid to its executives. The
      Company's bonus system is a discretionary annual performance-based
      incentive bonus system, approved by the Company's Board, and is based upon
      a combination of personal and corporate performance contributing to your
      maximum target. Bonuses are determined in December of each year.

            (c) Equity Compensation.

                  (i) Initial Grant. On the Effective Date and pursuant to a
            written stock option agreement (the "Stock Option Agreement")
            between the Company


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            and you under the OSI Pharmaceuticals, Inc. Amended and Restated
            Stock Incentive Plan (the "Plan"), you will be granted a
            non-qualified option (the "Initial Option") to purchase 150,000
            shares of the Company's common stock, par value, $.01 per share (the
            "Common Stock"). The exercise price for the Initial Option will be
            the fair market value per share of the Common Stock on the date the
            Initial Option is granted and the other terms and conditions of the
            Initial Option will be as set forth in the Plan and the Stock Option
            Agreement. The Initial Option will have a term of 10 years and will
            become exercisable with respect to 33% of such shares on the first
            anniversary of the date of grant with the remaining shares vesting
            over the succeeding 48 months following the first anniversary of the
            date of grant on a monthly pro-rated basis. Notwithstanding the
            foregoing, the Initial Option shall vest and be fully exercisable
            upon a Change of Control (as hereinafter defined).

                  (ii) Future Grants. On each date that annual stock options or
            other equity compensation are granted by the Company to its
            executive management group, so long as you then remain in the employ
            of the Company, the Company will grant to you an option (an "Annual
            Option") to purchase a number of shares of Common Stock to be
            determined by the Compensation Committee of the Board based upon
            your grade level. The exercise price for each Annual Option will be
            the fair market value per share of Common Stock on the date the
            Annual Option is granted and the other terms and conditions of the
            Annual Option will be as set forth in the Plan and Option Agreement
            accompanying such Annual Option. Notwithstanding the foregoing, each
            Annual Option shall vest and be fully exercisable upon a Change of
            Control (as hereinafter defined).

                  (iii) Restricted Stock Grant. On the first business day of the
            month after your employment begins, pursuant to the terms of the
            Plan, the Company will issue to you 15,000 shares of Common Stock
            ("Restricted Stock"). The shares of Restricted Stock shall vest in
            five equal tranches of 3,000 shares on each anniversary of the date
            of issuance commencing with June 1, 2006, provided that you continue
            to be an employee of the Company or an affiliate or subsidiary of
            the Company as of such date. Notwithstanding the foregoing, all of
            the shares of Restricted Stock shall vest upon a Change of Control.
            The terms and conditions of the Restricted Stock will be set forth
            in a Restricted Stock Agreement.

            (d) Vacation. You will be entitled to 22 paid vacation days in each
      calendar year, and paid holidays plus personal days in accordance with the
      Company's policies for its senior executives as in effect from time to
      time.

            (e) Fringe Benefits. In addition to the equity compensation provided
      for herein, you will be entitled to participate in employee benefit plans
      which the Company provides or may establish for the benefit of its senior
      executives generally (for example, term life, disability, medical, dental
      and other insurance, retirement, pension, profit-sharing and similar
      plans) (collectively, the "Fringe Benefits"). Your eligibility to
      participate in the Fringe Benefits and receive benefits thereunder will be
      subject to the plan documents


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      governing such Fringe Benefits. Nothing contained herein will require the
      Company to establish or maintain any Fringe Benefits.

            (f) Relocation. The Company will assist you in your relocation to
      Long Island in accordance with the following:

                  (i) Relocation Service. American International will assist you
            in your relocation from New Jersey to Long Island.

                  (ii) Current Residence. The Company, through American
            International and at your request, will appraise your current
            residence in New Jersey. American International will arrange for two
            or more independent appraisals of your residence. You will market
            your home with their assistance to try to find a third-party buyer.
            If the sale price is less than the average of the appraisals, OSI
            will reimburse you the difference.

                  (iii) Expenses. The Company will reimburse you, either
            directly or through its relocation service, American International,
            for all expenses relating to your relocation from New Jersey to Long
            Island, including, without limitation, expenses relating to packing
            and moving household goods, temporary storage of household goods,
            closing costs (including 2 mortgage points) associated with the
            purchase of a new home on Long Island, sales and closing costs
            associated with the sale of your home in New Jersey, expenses
            incurred by you and/or your family relating to house-hunting trips
            (including transportation, hotel accommodations and meals) and
            expenses incurred by you and/or your family for temporary living
            accommodations for up to six months prior to your move into a new
            home (including transportation, lease or sublease amounts,
            utilities, hotel or other accommodations, brokers' fees). During the
            six-month period commencing with the Effective Date, the Company
            will pay for a car service to bring you to and from Long Island on
            Mondays and Fridays.

                  (iv) Mortgage Assistance. For a period of three years
            following your purchase of a home on Long Island (the "Long Island
            Home"), the Company will pay you a mortgage assistance allowance
            equal to $50,000 per annum, payable in equal monthly installments.
            The foregoing is subject to your continued employment with the
            Company during such three-year period. If (A) your employment
            terminates "without cause" (as defined in Section 4(e) hereof), (B)
            you terminate your employment for "good reason" (as defined in
            Section 4(d) hereof), or (C) upon a "Change of Control" (as defined
            in Section 7 hereof) prior to the end of such three-year period, you
            will continue to receive such mortgage assistance allowance on the
            terms described in this section provided that you remain resident in
            the Long Island Home.

                  (v) Lump Sum Payment.In addition to the amounts provided for
            in Sections 3 (f) (iii) and (iv), upon your purchase of the Long
            Island Home, you will receive a one-time lump sum payment equal to
            $25,000 to cover incidental expenses.


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                  (vi) Additional Living Expenses. If you have not relocated to
            Long Island on or before November 30, 2005, the Company will
            continue to pay for a car service to bring you to and from Long
            Island on Mondays and Fridays and to reimburse you for your living
            expenses; provided, however, that such costs will be offset against
            the amounts which are otherwise to be subsequently reimbursed to you
            pursuant to Section (f) (ii) and (iii) upon your ultimate relocation
            to Long Island (e.g., moving costs, spread between the appraised
            value and the sale price of your New Jersey home, etc.) provided
            that the amount to be reimbursed under Section (f) (ii) and (iii) is
            greater than the offsetting amount. In the event that the amount to
            be reimbursed to you pursuant to Section (f) (ii) and (iii) is less
            than the amount to be reimbursed under this Section (f) (vi), you
            will not be required to pay back to the Company the difference
            between the two amounts.

                  (vii) Pay-Back. If, within 12 months following the Effective
            Date, you terminate your employment with the Company "without good
            reason" (as defined in Section 4(f) hereof), you shall pay back all
            (based upon the date of your termination) of the amounts paid to you
            pursuant to Sections 3 (f) (iii), (iv), (v) and (vi) (the
            "Relocation Expenses").

                  (viii) Documentation. Reimbursement of the expenses provided
            for in this Section 3(f) shall be made upon presentation of
            documentation reasonably satisfactory to the Company in accordance
            with the Company's policies with respect thereto as in effect from
            time to time. Receipts shall not be required for payment covered
            under Section 3 (f) (v).

                  (ix) Any amounts paid under this Section 3 (f) deemed to be
            taxable income to you will be grossed up for taxes at the
            appropriate rate.

            (g) Reimbursement of Expenses. Upon presentation of documentation of
      such expenses reasonably satisfactory to the Company, the Company will
      reimburse you for all ordinary and reasonable out-of-pocket business
      expenses that are reasonably incurred by you in furtherance of the
      Company's business in accordance with the Company's policies with respect
      thereto as in effect from time to time.

      4. Termination. The Employment Term shall end upon the earliest of the
      following to occur:

            (a) Your death.

            (b) Upon written notice to you of termination as a result of your
      Permanent Disability. "Permanent Disability" means your inability, by
      reason of any physical or mental impairment, to substantially perform your
      duties and responsibilities hereunder for two or more periods of 90 days
      each in any 360-day period, as determined by a qualified physician with no
      history of prior dealings with you or the Company, as reasonably agreed
      upon by you (or, if you are unable to make such selection, by an adult


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      member of your immediate family) and the Company. Such physician's written
      determination of your Permanent Disability shall, upon delivery to the
      Company, be final and conclusive for purposes of this Agreement.

            (c) Your termination by the Company for "cause" as evidenced by, and
      effective upon, delivery by the Company to you of a Notice of Termination
      (as defined in Section 5 below). "Cause" shall mean, for purposes of this
      Agreement, (i) an act of fraud or embezzlement against the Company or an
      unauthorized disclosure of Confidential Information (as defined in Section
      8(a)(iv) hereof) of the Company, in each case which is willful and results
      in material damage to the Company, (ii) any criminal violation of the
      Securities Act of 1933 or the Securities Exchange Act of 1934, (iii) your
      conviction (or a plea of nolo contendere) of any felony, (iv) your gross
      neglect of your duties or your willful and continuing refusal to perform
      your duties, provided you have been given written notice of such neglect
      or refusal and within 30 days have failed to cure such neglect and
      refusal, or (v) your material willful misconduct with respect to the
      business or affairs of the Company.

            (d) Your termination of your employment for "good reason" by
      delivering to the Company a Notice of Termination (as defined in Section 5
      below) not less than 30 days prior to the effective date of such
      termination. For purposes of this Agreement, "good reason" shall mean the
      occurrence of any of the events hereinafter set forth which are not cured
      by the Company within 30 days after the Company has received written
      notice from you specifying the particular events or conditions which
      constitute "good reason":

                  (i) a material reduction in your duties, title,
            responsibilities, authority, status, or reporting responsibilities
            unless you have previously consented in writing to such reduction
            (which consent may be given or withheld in your sole discretion);

                  (ii) a material reduction in your Base Salary or the range of
            your target bonus;

                  (iii) the Company's requiring you to be based more than 35
            miles from the Company's current headquarters in Melville, New York
            or to any location for which the average commute from your residence
            exceeds 45 minutes; or


                  (iv) change of control (as defined in Section 7 hereof).

            (e) Termination of your employment by the Company "without cause" by
      delivery by the Company to you of a Notice of Termination (as defined in
      Section 5 below) not less than 30 days prior to the effective date of such
      termination. Your termination by the Company shall be considered to be
      "without cause" if you are terminated or dismissed by the Company for
      reasons other than death, Permanent Disability or for "cause".


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            (f) Your termination of your employment "without good reason" by
      delivery by you to the Company of a Notice of Termination (as defined in
      Section 5 below). Your termination of your employment shall be considered
      to be "without good reason" unless you resign for "good reason" (as
      defined in Section 4(d)).

      5. Notice of Termination. Any termination by the Company or by you shall
      be communicated by a written "Notice of Termination" to the other party
      hereto. A "Notice of Termination" shall mean a notice which indicates a
      termination date and the specific termination provision in this Agreement
      relied upon and which sets forth in reasonable detail the facts and
      circumstances claimed to provide a basis for termination under the
      provision so indicated.

      6. Payments Upon Termination.

            (a) Upon termination of your employment for any reason you will
      become entitled to (i) any accrued and unpaid Base Salary up to the date
      of termination, and (ii) any accrued and unpaid vacation pay up to the
      date of termination ((i) and (ii) being collectively referred to as the
      "Accrued Compensation").

            (b) Upon termination of your employment due to death or Permanent
      Disability, in addition to Accrued Compensation, you (or your estate, as
      the case may be) will become entitled to an amount equal to the bonus that
      you would have been entitled to receive for the fiscal year in which your
      termination occurs had you continued to be employed until the end of such
      fiscal year, multiplied by a fraction (i) the numerator of which is the
      number of days in such fiscal year through the termination date and (ii)
      the denominator or which is 365 (a "Pro-rata Bonus").

            (c) Upon a termination of your employment by the Company "without
      cause" or by you "for good reason" or upon a "Change of Control" (as
      defined in Section 7 hereof), in addition to Accrued Compensation, you
      will become entitled to (i) your Base Salary for 12 months following the
      date of termination, (ii) your Pro-rata Bonus, and (iii) continued
      coverage for 12 months following termination under any health and dental
      program in which you were eligible to participate as of the time of
      termination of your employment.

            (d) You shall not be required to mitigate the amount of any payment
      provided for under this Section 6 by seeking other employment or otherwise
      and no payment shall be offset or reduced by the amount of any
      compensation or benefits provided to you in any subsequent employment. The
      Company's obligation to make the payments provided for in this Section 6
      and otherwise perform its obligations hereunder shall not be affected by
      any circumstances, including, without limitation, set-off, counterclaim,
      recoupment, defense or other claim, right or action which the Company may
      have against you or others.


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      7. Change of Control. For purposes of this Agreement, a "Change of
      Control" shall mean the approval by stockholders of the Company of (a) a
      merger or consolidation involving the Company if the stockholders of the
      Company, immediately before such merger or consolidation, do not, as a
      result of such merger or consolidation, directly or indirectly, continue
      to hold greater than 60% of the voting power in the resulting entity, or
      (b) an agreement for the sale or other disposition of all or substantially
      all of the assets of the Company.

      8. Prohibited Activities.

            (a) Certain Acknowledgements and Agreements.

                  (i) We have discussed, and you recognize and acknowledge the
            competitive and proprietary aspects of the business of the Company.

                  (ii) You acknowledge that your employment by the Company
            creates a relationship of confidence and trust between the Company
            and you with respect to certain information relating to the business
            and affairs of the Company or applicable to the business of any
            client, customer, consultant, partner, external collaborator or
            service provider of the Company, which may be made known to you by
            the Company or by any client, customer, consultant, partner,
            external collaborator or service provider of the Company, or learned
            by you during the period of your affiliation with the Company.

                  (iii) You further acknowledge that, while you are employed
            hereunder, the Company will furnish, disclose or make available to
            you Confidential Information (as defined in Section 8 (a) (iv)
            below) related to the business of the Company (whether or not the
            information has commercial value to the Company's business). You
            also acknowledge that such Confidential Information has been
            developed and will be developed by the Company through the
            expenditure by the Company of substantial time, effort and money and
            that all such Confidential Information could be used by you to
            compete with the Company. You also acknowledge that if you become
            employed or affiliated with any competitor of the Company, it is
            possible that you would disclose Confidential Information to such
            competitor and would use Confidential Information, knowingly or
            unknowingly, on behalf of such competitor.

                  (iv) For purposes of this Agreement, "Confidential
            Information" means confidential and proprietary information of the
            Company, whether in written, oral, electronic or other form,
            including, without limitation, systems, processes, formulae, data,
            functional specifications, computer software, programs and displays,
            know-how, improvements, discoveries, inventions, developments,
            designs, techniques, marketing plans, strategies, forecasts, new and
            proposed products and technologies, unpublished financial statements
            and financial information, business plans, budgets, projections,
            licenses, prices, costs, training methods and materials, sales
            prospects, and customer, supplier, manufacturer,


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            collaborator, partner, and client lists and any and all intellectual
            properties, including any scientific, technical or trade secrets of
            the Company or of any third party provided to you or the Company
            under a condition of confidentiality, provided that Confidential
            Information will not include information that is in the public
            domain other than through any fault or act by you.

            (b) Covenants. While you are employed hereunder and for a period of
      one year following the termination of your employment hereunder for any
      reason or for no reason, you will not, without the prior written consent
      of the Company:

                  (i) Engage, directly or indirectly, for your benefit or the
            benefit of others, in any activity or employment in the performance
            of which any Confidential Information obtained during the course of
            your employment would, by necessity, need to be disclosed by you in
            order to engage in any such activity or employment. This covenant
            shall not be construed to limit in any way your obligation not to
            use or disclose Confidential Information as set forth in Section 9
            below.

                  (ii) Either individually or on behalf of or through any third
            party, directly or indirectly, solicit, divert or appropriate or
            attempt to solicit, divert or appropriate, any customers of the
            Company or any prospective customers with respect to which the
            Company has developed or made a sales presentation (or similar
            offering of services) for the purpose of directly competing with the
            Company with respect to the Company's "principal marketed products"
            (i.e., those products which are in the first or second detail
            position) or its development candidates which have material
            financial significance to the Company and which are in Phase III
            programs; or

                  (iii) Either individually or on behalf of or through any third
            party, directly or indirectly, (A) solicit, entice or persuade or
            attempt to solicit, entice or persuade any employees of or
            consultants to the Company to leave the service of the Company for
            any reason, or (B) employ, cause to be employed, or solicit the
            employment of, any employees of or consultants to the Company while
            any such person is providing services to the Company or within six
            months after any such person has ceased providing services to the
            Company; or

                  (iv) Either individually or on behalf of or through any third
            party, directly or indirectly, interfere with, or attempt to
            interfere with, the relations between the Company and any
            manufacturer or supplier to or customer of the Company.

            (c) Reasonableness of Restrictions. You understand that the
      provisions set forth in Section 8(b) are not meant to prevent you from
      earning a living or fostering your career. They are intended, however, to
      prevent competitors of the Company from gaining an unfair advantage from
      your knowledge of Confidential Information. You understand that, by making
      any other employer aware of the provisions set forth in this Section 8,
      that employer can take such action as to avoid your breach of this Section
      8.


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            (d) Survival of Acknowledgements and Agreements. Your
      acknowledgements and agreements set forth in this Section 8 will survive
      the termination of this Agreement and the termination of your employment
      hereunder for any reason or for no reason.

      9. Protected Information. All Confidential Information shall be the sole
      property of the Company and its assigns. You hereby assign to the Company
      any right you may have or acquire in such Confidential Information. You
      will at all times, both during the period while you are employed hereunder
      and after the termination of this Agreement and the termination of your
      employment hereunder for any reason or for no reason, maintain in
      confidence and will not, without the prior written consent of the Company,
      use, except as required in the course of performance of your duties for
      the Company or by court order, disclose or give to others any Confidential
      Information. In the event you are questioned by anyone not employed by the
      Company or by an employee of or a consultant to the Company not authorized
      to receive Confidential Information, in regard to any Confidential
      Information, or concerning any fact or circumstance relating thereto, you
      will promptly notify the Company. Upon the termination of your employment
      hereunder for any reason or for no reason, or if the Company otherwise
      requests, you will return to the Company all tangible Confidential
      Information and copies thereof (regardless how such Confidential
      Information or copies are maintained). The terms of this Section 9 are in
      addition to, and not in lieu of, any statutory or other contractual or
      legal obligation that you may have relating to the protection of the
      Company's Confidential Information. The terms of this Section 9 will
      survive indefinitely any termination of this Agreement and/or any
      termination of your employment hereunder for any reason or for no reason.

      10. Ownership of Ideas, Copyrights and Patents.

            (a) Property of the Company. All ideas, discoveries, creations,
      manuscripts and properties, innovations, improvements, know-how,
      inventions, designs, developments, apparatus, techniques, methods,
      biological processes, cell lines, laboratory notebooks and formulae
      (collectively, the "Inventions") which may be used in the current or
      planned business of the Company or which in any way relates to such
      business, whether patentable, copyrightable or not, which you may
      conceive, reduce to practice or develop while you are employed hereunder
      (and, if based on or related to any Confidential Information, within two
      years after termination of such employment for any reason or for no
      reason), alone or in conjunction with another or others, whether during or
      out of regular business hours, whether or not on the Company's premises or
      with the use of its equipment, and whether at the request or upon the
      suggestion of the Company or otherwise, will be the sole and exclusive
      property of the Company, and that you will not publish any of the
      Inventions without the prior written consent of the Company. Without
      limiting the foregoing, you also acknowledge that all original works of
      authorship which are made by you (solely or jointly with others) within
      the scope of your employment or which relate to the business of the
      Company and which are protectable by copyright are "works made for hire"
      pursuant to the United States Copyright Act (17 U.S.C. Section 101). You
      will promptly disclose to the Company all of the foregoing and you hereby
      assign to the Company all of your right, title and interest in and to all
      of the


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      foregoing. You further represent that, to the best of your knowledge and
      belief, none of the Inventions will violate or infringe upon any right,
      patent, copyright, trademark or right of privacy, or constitute libel or
      slander against or violate any other rights of any person, firm or
      corporation, and that you will use your best efforts to prevent any such
      violation.

            (b) Cooperation. At any time during your employment hereunder or
      after the termination of your employment hereunder for any reason or for
      no reason, you will cooperate fully with the Company and its attorneys and
      agents in the preparation and filing of all papers and other documents as
      may be required to perfect the Company's rights in and to any of such
      Inventions, including, without limitation, joining in any proceeding to
      obtain letters patent, copyrights, trademarks or other legal rights with
      respect to any such Inventions in the United States and in any and all
      other countries, provided that the Company will bear the expense of such
      proceedings, and that any patent or other legal right so issued to you
      personally will be assigned by you to the Company without charge by you.

            (c) Licensing and Use of Inventions. With respect to any Inventions,
      and work of any similar nature (from any source), whenever created, which
      you have not prepared or originated in the performance of your employment,
      but which you provide to the Company or incorporate in any Company product
      or system, you hereby grant to the Company a royalty-free, fully paid-up,
      non-exclusive, perpetual and irrevocable license throughout the world to
      use, modify, create derivative works from, disclose, publish, translate,
      reproduce, deliver, perform, dispose of, and to authorize others so to do,
      all such Inventions. You will not include in any Inventions you deliver to
      the Company or use on its behalf, without the prior written approval of
      the Company, any material which is or will be patented, copyrighted or
      trademarked by you or others unless you provide the Company with the
      written permission of the holder of any patent, copyright or trademark
      owner for the Company to use such material in a manner consistent with
      then-current Company policy.

            (d) Prior Inventions. Listed on Exhibit 10(d) to this Agreement are
      any and all Inventions in which you claim or intend to claim any right,
      title and interest (collectively, "Prior Inventions"), including, without
      limitation, patent, copyright and trademark interests, which to the best
      of your knowledge will be or may be delivered to the Company in the course
      of your employment, or incorporated into any Company product or system.
      You acknowledge that your obligation to disclose such information is
      ongoing while you are employed hereunder.

      11. Records. Upon termination of your employment hereunder for any reason
      or for no reason and at any other time requested by the Company, you will
      deliver to the Company any property of the Company which may be in your
      possession, including products, materials, memoranda, notes, records,
      reports, or other documents or photocopies of the same.

      12. Representations. You hereby represent and warrant to the Company that
      you understand this Agreement, that you enter into this Agreement
      voluntarily and that your


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      employment under this Agreement will not conflict with any legal duty owed
      by you to any other party, or with any agreement to which you are a party
      or by which you are bound, including, without limitation, any
      non-competition or non-solicitation provision contained in any such
      agreement.

      13. General.

            (a) Notices. All notices, requests, consents and other
      communications hereunder which are required to be provided, or which the
      sender elects to provide, in writing, will be addressed to the receiving
      party's address set forth above or to such other address as a party may
      designate by notice hereunder, and will be either (i) delivered by hand,
      (ii) sent by overnight courier, or (iii) sent by registered or certified
      mail, return receipt requested, postage prepaid. All notices, requests,
      consents and other communications hereunder will be deemed to have been
      given either (i) if by hand, at the time of the delivery thereof to the
      receiving party at the address of such party set forth above, (ii) if sent
      by overnight courier, on the next business day following the day such
      notice is delivered to the courier service, or (iii) if sent by registered
      or certified mail, on the fifth business day following the day such
      mailing is made.

            (b) Entire Agreement. This Agreement, and the other agreements
      specifically referred to herein, embodies the entire agreement and
      understanding between the parties hereto with respect to the subject
      matter hereof and supersedes all prior oral or written agreements and
      understandings relating to the subject matter hereof. No statement,
      representation, warranty, covenant or agreement of any kind not expressly
      set forth in this Agreement will affect, or be used to interpret, change
      or restrict, the express terms and provisions of this Agreement.

            (c) Modifications and Amendments. The terms and provisions of this
      Agreement may be modified or amended only by written agreement executed by
      the parties hereto.

            (d) Waivers and Consents. The terms and provisions of this Agreement
      may be waived, or consent for the departure therefrom granted, only by
      written document executed by the party entitled to the benefits of such
      terms or provisions. No such waiver or consent will be deemed to be or
      will constitute a waiver or consent with respect to any other terms or
      provisions of this Agreement, whether or not similar. Each such waiver or
      consent will be effective only in the specific instance and for the
      purpose for which it was given, and will not constitute a continuing
      waiver or consent.

            (e) Assignment. The Company may assign its rights and obligations
      hereunder to any person or entity that succeeds to all or substantially
      all of the Company's business or that aspect of the Company's business in
      which you are principally involved or to any Company Affiliate; provided,
      that the Company shall remain responsible for any payments and obligations
      to you to the extent any assignee fails to fulfill such payments and
      obligations. You may not assign your rights and obligations under this
      Agreement without the prior written consent of the Company and any such
      attempted assignment by you without the prior written consent of the
      Company will be void.


                                       12
<PAGE>

            (f) Benefit. All statements, representations, warranties, covenants
      and agreements in this Agreement will be binding on the parties hereto and
      will inure to the benefit of the respective successors and permitted
      assigns of each party hereto. Nothing in this Agreement will be construed
      to create any rights or obligations except between the Company and you,
      except for your obligations to the Company as set forth herein, and no
      person or entity (except for a Company Affiliate as set forth herein) will
      be regarded as a third-party beneficiary of this Agreement.

            (g) Governing Law. This Agreement and the rights and obligations of
      the parties hereunder will be construed in accordance with and governed by
      the laws of the State of New York, without giving effect to the conflict
      of law principles thereof.

            (h) Jurisdiction, Venue and Service of Process. Any legal action or
      proceeding with respect to this Agreement that is not subject to
      arbitration pursuant to Section 14 (i) below will be brought in the courts
      of Suffolk County, New York. By execution and delivery of this Agreement,
      each of the parties hereto accepts for itself and in respect of its
      property, generally and unconditionally, the exclusive jurisdiction of the
      aforesaid courts.

            (i) Arbitration. Any controversy, dispute or claim arising out of or
      in connection with this Agreement, other than a controversy, dispute or
      claim arising under Section 8, 9 or 10 hereof, will be settled by final
      and binding arbitration to be conducted in New York, New York pursuant to
      the national rules for the resolution of employment disputes of the
      American Arbitration Association then in effect. The decision or award in
      any such arbitration will be final and binding upon the parties and
      judgment upon such decision or award may be entered in any court of
      competent jurisdiction or application may be made to any such court for
      judicial acceptance of such decision or award and an order of enforcement.
      In the event that any procedural matter is not covered by the aforesaid
      rules, the procedural law of New York will govern. Any disagreement as to
      whether a particular dispute is arbitrable under this Agreement shall
      itself be subject to arbitration in accordance with the procedures set
      forth herein. The fees of the arbitrators shall be paid by the Company.

            (j) WAIVER OF JURY TRIAL. ANY ACTION, DEMAND, CLAIM OR COUNTERCLAIM
      ARISING UNDER OR RELATING TO THIS AGREEMENT THAT IS NOT SUBJECT TO
      ARBITRATION PURSUANT TO SECTION 14(i) ABOVE WILL BE RESOLVED BY A JUDGE
      ALONE AND EACH OF YOU AND THE COMPANY WAIVE ANY RIGHT TO A JURY TRIAL
      THEREOF.

            (k) Severability. The parties intend this Agreement to be enforced
      as written. However, (i) if any portion or provision of this Agreement is
      to any extent declared illegal or unenforceable by a duly authorized court
      having jurisdiction, then the remainder of this Agreement, or the
      application of such portion or provision in circumstances other than those
      as to which it is so declared illegal or unenforceable, will not be
      affected thereby, and each portion and provision of this Agreement will be
      valid and enforceable to the fullest extent permitted by law and (ii) if
      any provision, or part thereof, is held to be unenforceable because of the
      duration of such provision, the geographic area covered thereby, or other
      aspect or scope of such provision, the court making such determination
      will have the power


                                       13
<PAGE>

      to reduce the duration, geographic area of such provision, or other aspect
      or scope of such provision, and/or to delete specific words and phrases
      ("blue-penciling"), and in its reduced or blue-penciled form, such
      provision will then be enforceable and will be enforced.

            (l) Injunctive Relief. You hereby expressly acknowledge that any
      breach or threatened breach of any of the terms and/or conditions set
      forth in Section 8, 9 or 10 of this Agreement will result in substantial,
      continuing and irreparable injury to the Company. Therefore, in addition
      to any other remedy that may be available to the Company, the Company will
      be entitled to injunctive or other equitable relief by a court of
      appropriate jurisdiction in the event of any breach or threatened breach
      of the terms of Section 8, 9 or 10 of this Agreement. The period during
      which the covenants contained in Section 8 will apply will be extended by
      any periods during which you are found by a court to have been in
      violation of such covenants.

            (m) No Waiver of Rights, Powers and Remedies. No failure or delay by
      a party hereto in exercising any right, power or remedy under this
      Agreement, and no course of dealing between the parties hereto, will
      operate as a waiver of any such right, power or remedy of the party. No
      single or partial exercise of any right, power or remedy under this
      Agreement by a party hereto, nor any abandonment or discontinuance of
      steps to enforce any such right, power or remedy, will preclude such party
      from any other or further exercise thereof or the exercise of any other
      right, power or remedy hereunder. The election of any remedy by a party
      hereto will not constitute a waiver of the right of such party to pursue
      other available remedies. No notice to or demand on a party not expressly
      required under this Agreement will entitle the party receiving such notice
      or demand to any other or further notice or demand in similar or other
      circumstances or constitute a waiver of the rights of the party giving
      such notice or demand to any other or further action in any circumstances
      without such notice or demand.

            (n) Counterparts. This Agreement may be executed in two or more
      counterparts, and by different parties hereto on separate counterparts,
      each of which will be deemed an original, but all of which together will
      constitute one and the same instrument.

            (o) Opportunity to Review. You hereby acknowledge that you have had
      adequate opportunity to review these terms and conditions and to reflect
      upon and consider the terms and conditions of this Agreement, and that you
      have had the opportunity to consult with counsel of your own choosing
      regarding such terms. You further acknowledge that you fully understand
      the terms of this Agreement and have voluntarily executed this Agreement.

            (p) Survival of the Company's Obligations. Notwithstanding the
      termination of this agreement pursuant to Section 4, the Company's
      obligation to make payments and provide benefits to you as set forth in
      Section 3 (f) (iv) and Section 6 will remain in effect.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]


                                       14
<PAGE>


      If the foregoing accurately sets forth our agreement, please so indicate
by signing and returning to us the enclosed copy of this Agreement.



                                       Very truly yours,


                                       OSI Pharmaceuticals, Inc.

                                       By: /s/ Colin Goddard
                                          -----------------------------
                                       Name:    Colin Goddard, Ph.D
                                       Title:   Chief Executive Officer

Accepted and Approved:


/s/ Michael Atieh
---------------------------            ---------
Michael Atieh                          Date


                                       15
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                                  EXHIBIT 10(d)

                                PRIOR INVENTIONS


                                       N/A




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