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                                                                    EXHIBIT 4.5

                                                                  EXECUTION COPY

                            ACCOUNT CONTROL AGREEMENT

          ACCOUNT CONTROL AGREEMENT (this "AGREEMENT") dated as of February 1,
2002, among OSI Pharmaceuticals, Inc., a Delaware corporation (the "PLEDGOR"),
The Bank of New York, a New York banking corporation, as Trustee (the "SECURED
PARTY"), and The Bank of New York, a New York banking corporation, as securities
intermediary and depository bank (the "ACCOUNT HOLDER").

PRELIMINARY STATEMENTS:

          (1)   The Pledgor has granted the Secured Party a security interest
(the "SECURITY INTEREST") in certain security entitlements (the "PLEDGED
SECURITY ENTITLEMENTS") with respect to certain U.S. Treasury securities (the
"PLEDGED FINANCIAL ASSETS") identified on Schedule I attached hereto maintained
by the Pledgor with the Account Holder and carried from time to time in an
account with the Account Holder, ABA No. 021000018, Account No. 341431 at its
office at 101 Barclay Street, New York, New York 10286, in the name of "OSI
Pharmaceuticals Pledge Account" (the "ACCOUNT") and all additions thereto and
substitutions and proceeds thereof, pursuant to, and as more particularly
described in, a Collateral Pledge and Security Agreement dated as of February 1,
2002, among the Pledgor and the Trustee (as the same may hereafter be amended,
supplemented or otherwise modified from time to time, the "PLEDGE AGREEMENT";
terms defined in the Pledge Agreement and not otherwise defined herein being
used herein as therein defined). The Pledgor acknowledges having received value
for such pledge.

          (2)   Terms defined in Article 8 or 9 of the Uniform Commercial Code
in effect in the State of New York ("N.Y. UNIFORM COMMERCIAL CODE") are used in
this Agreement as such terms are defined in such Article 8 or 9.

          (3)   The Pledgor, the Trustee and the Account Holder are delivering
this Agreement pursuant to the terms of Section 4(f) of the Pledge Agreement.

          NOW, THEREFORE, in consideration of the premises and of the mutual
agreements contained herein, the parties hereto hereby agree as follows:

          SECTION 1. THE ACCOUNTS. The Account Holder represents and warrants
to, and agrees with, the Secured Party that:

          (a)   The Account Holder maintains the Account for the Pledgor, and
     all the Pledged Financial Assets and all additions thereto and
     substitutions and proceeds thereof held by the Account Holder for the
     account of the Pledgor are, and will continue to be, credited to the
     Account.

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          (b)   To the extent that funds are credited to the Account, the
     Account is a deposit account; and to the extent that financial assets are
     credited to the Account, the Account is a securities account. The Account
     Holder is (i) the bank with which the Account is maintained and (ii) the
     securities intermediary with respect to financial assets held in the
     Account. The Pledgor is (x) the Account Holder's customer with respect to
     the Account and (y) the entitlement holder with respect to financial assets
     credited from time to time to the Account.

          (c)   Notwithstanding any other agreement to the contrary, the Account
     Holder's jurisdiction with respect to the Account for purposes of the N.Y.
     Uniform Commercial Code is, and will continue to be for so long as the
     Security Interest shall be in effect, the State of New York.

          (d)   Attached as Exhibit A hereto is the statement of the Account as
     of the date hereof showing the property credited to the Account.

          (e)   The Account Holder does not know of any claim to or interest in
     the Account or any property (including, without limitation, funds and
     financial assets) credited to the Account, except for claims and interests
     of the parties referred to in this Agreement.

          SECTION 2. CONTROL BY SECURED PARTY. The Account Holder will comply
with (i) all instructions directing disposition of the funds in the Account,
(ii) all notifications and entitlement orders that the Account Holder receives
directing it to transfer or redeem any financial asset in the Account, and (iii)
all other directions concerning the Account, including, without limitation,
directions to distribute to the Secured Party proceeds of any such transfer or
redemption or interest or dividends on property in the Account (any such
instruction, notification or direction referred to in clause (i), (ii) or (iii)
above being an "ACCOUNT DIRECTION"), in each case of clauses (i), (ii) and (iii)
above originated by the Secured Party without further consent by the Pledgor or
any other Person. The Account Holder will comply with Account Directions and
other directions concerning the Account originated by, and only by, the Secured
Party. The Account Holder acknowledges that the Secured Party has exclusive
control over the Account and all Pledged Financial Assets contained therein from
time to time.

          SECTION 3. PRIORITY OF SECURED PARTY'S SECURITY INTEREST.

          (a)   The Account Holder (i) subordinates to the Security Interest and
     in favor of the Secured Party any security interest, lien, or right of
     recoupment or setoff that the Account Holder may have, now or in the
     future, against the Account or any property (including, without limitation,
     any funds and financial assets) credited to the Account, and (ii) agrees
     that it will not exercise any right in respect of any such security
     interest or lien or any such right of recoupment or setoff until the
     Security Interest is terminated, EXCEPT that the Account Holder (A) will
     retain its prior security interest and lien on property credited to
     the Account, (B) may exercise any right in respect of such security
     interest or lien, and (C) may exercise any right of recoupment or setoff
     against the Account, in the case of clauses (A), (B) and (C) above, to
     secure or to satisfy, and only to secure or to satisfy, payment (x) for
     such property, (y) for its customary fees and

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     expenses for the routine maintenance and operation of the Account, and (z)
     if the Account is a deposit account, for the face amount of any items that
     have been credited to the Account but are subsequently returned unpaid
     because of uncollected or insufficient funds.

          (b)   The Account Holder will not enter into any other agreement with
     any Person relating to Account Directions or other directions with respect
     to the Account.

          SECTION 4. STATEMENTS, CONFIRMATIONS, AND NOTICES OF ADVERSE CLAIMS.

          (a)   The Account Holder will send copies of all statements and
     confirmations for the Account simultaneously to the Secured Party and the
     Pledgor.

          (b)   When the Account Holder knows of any claim or interest in the
     Account or any property (including, without limitation, funds and financial
     assets) credited to the Account other than the claims and interests of the
     parties referred to in this Agreement, the Account Holder will promptly
     notify the Secured Party and the Pledgor of such claim or interest.

          SECTION 5. THE ACCOUNT HOLDER'S RESPONSIBILITY.

          (a)   The Account Holder will be liable to the Secured Party for
     complying with Account Directions or other directions concerning the
     Account from the Pledgor or any Person other than the Secured Party.

          (b)   The Account Holder will not be liable to the Pledgor or the
     Secured Party for complying with an Account Direction or other direction
     concerning the Account originated by the Secured Party, even if the Pledgor
     notifies the Account Holder that the Secured Party is not legally entitled
     to issue the Account Direction or such other direction unless the Account
     Holder takes the action after it is served with an injunction, restraining
     order, or other legal process enjoining it from doing so, issued by a court
     of competent jurisdiction, and had a reasonable opportunity to act on the
     injunction, restraining order or other legal process.

          (c)   This Agreement does not create any obligation of the Account
     Holder except for those expressly set forth in this Agreement and, to the
     extent that the Account is a securities account, in Part 5 of Article 8 of
     the N.Y. Uniform Commercial Code and, to the extent that the Account is a
     deposit account, in Article 4 of the N.Y. Uniform Commercial Code. In
     particular, the Account Holder need not investigate whether the Secured
     Party is entitled under the Secured Party's agreements with the Pledgor to
     give an Account Direction or other direction concerning the Account. The
     Account Holder may rely on notices and communications it believes given by
     the appropriate party.

          SECTION 6. INDEMNITY. The Pledgor will indemnify the Account Holder,
its officers, directors, employees and agents against claims, liabilities and
expenses arising out of this Agreement (including, without limitation,
reasonable attorney's fees and disbursements), except to the extent the claims,
liabilities or expenses are caused by the Account Holder's gross

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negligence or willful misconduct as found by a court of competent jurisdiction
in a final, non-appealable judgment.

          SECTION 7. TERMINATION; SURVIVAL.

          (a)   This Agreement shall terminate automatically upon receipt by the
     Account Holder of written notice executed by two officers of the Trustee
     that all of the Secured Obligations have been paid in full in cash or
     otherwise satisfied or all of the Collateral has been released, which ever
     is earlier, and the Account Holder shall thereafter be relieved of all
     duties and obligations hereunder.

          (b)   The Account Holder may terminate this Agreement on 60 days'
     prior notice to the Secured Party and the Pledgor, PROVIDED that before
     such termination the Account Holder and the Pledgor shall make arrangements
     to transfer the property (including, without limitation, all funds and
     financial assets) credited to the Account to another Account Holder that
     shall have executed, together with the Pledgor, a control agreement in
     favor of the Secured Party in respect of such property in substantially the
     form of this Agreement or otherwise in form and substance satisfactory to
     the Secured Party.

          (c)   Sections 5 and 6 will survive termination of this Agreement.

          SECTION 8. GOVERNING LAW. This Agreement and the Account will be
governed by the law of the State of New York. The Account Holder and the Pledgor
may not change the law governing the Account without the Secured Party's express
prior written agreement.

          SECTION 9. ENTIRE AGREEMENT. This Agreement is the entire agreement,
and supersedes any prior agreements, and contemporaneous oral agreements, of the
parties concerning its subject matter.

          SECTION 10. AMENDMENTS. No amendment of, or waiver of a right under,
this Agreement will be binding unless it is in writing and signed by the party
to be charged.

          SECTION 11. FINANCIAL ASSETS. The Account Holder agrees with the
Secured Party and the Pledgor that, to the fullest extent permitted by
applicable law, all property (other than funds) credited from time to time to
the Account will be treated as financial assets under Article 8 of the N.Y.
Uniform Commercial Code.

          SECTION 12. NOTICES. A notice or other communication to a party under
this Agreement will be in writing (except that Account Directions may be given
orally), will be sent to the party's address set forth under its name below or
to such other address as the party may notify the other parties and will be
effective on receipt.

          SECTION 13. BINDING EFFECT. This Agreement shall become effective when
it shall have been executed by the Pledgor, the Secured Party and the Account
Holder, and thereafter shall be binding upon and inure to the benefit of the
Pledgor, the Secured Party and the Account Holder and their respective
successors and assigns.

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          SECTION 14. EXECUTION IN COUNTERPARTS. This Agreement may be executed
in any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed shall be deemed to be an original
and all of which taken together shall constitute one and the same agreement.
Delivery of an executed counterpart of a signature page to this Agreement by
telecopier shall be effective as delivery of an original executed counterpart of
this Agreement.

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          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed by their respective officers thereunto duly authorized, as of the
date first above written.

                                       OSI PHARMACEUTICALS, INC.


                                       By /s/ ROBERT L. VAN NOSTRAND
                                          --------------------------
                                          Name:    Robert L. Van Nostrand
                                          Title:   Vice President and
                                                   Chief Financial Officer

                                       Address:
                                       58 South Service Road
                                       Melville, NY 11747

                                       THE BANK OF NEW YORK, as Trustee


                                       By /s/ JULIE SALOVITCH-MILLER
                                          --------------------------
                                          Name:    Julie Salovitch-Miller
                                          Title:   Vice President

                                       Address:
                                       5 Penn Plaza, 13th Floor
                                       New York, NY 10001

                                       THE BANK OF NEW YORK


                                       By /s/ GEOVANNI BARRIS
                                          Name:    Geovanni Barris
                                          Title:   Vice President

                                       Address:
                                       5 Penn Plaza, 13th Floor
                                       New York, NY 10001

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                                    EXHIBIT A

<Table>
<Caption>
                                                                   FACE AMOUNT
DESCRIPTION OF ASSET                          CUSIP NUMBER         OF ASSET
--------------------                          ------------         -----------
<S>                                             <C>                <C>
US TREASURY BILLS                               912795KU4          USD 4,000,000
US TREAS NTS SEC STRIPPED                       912833FR6          USD 4,000,000
US TREAS NTS SEC STRIPPED                       912833FS4          USD 4,000,000
UNITED STATES TREAS NT STRIPPED PRIN PMT        912820DJ3          USD 4,000,000
UNITED STATES TREAS NT STRP PRIN PMT            912820BJ5          USD 4,000,000
US TREASURY BD STRIPPED                         912803AB9          USD 4,000,000
</Table>