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                                                                    Exhibit 10.9

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.


                       ADDENDUM TO COLLABORATION AGREEMENT
                                      AMONG
                        MILLENNIUM PHARMACEUTICALS, INC.,
                              SCHERING CORPORATION
                            AND SCHERING-PLOUGH, LTD.


This addendum ("Addendum"), to be retroactively effective as of June 1, 2003
(the "Effective Date"), to the Collaboration Agreement by and among Millennium
Pharmaceuticals, Inc. ("Millennium"), as successor in interest to COR
Therapeutics, Inc., Schering Corporation, ("Schering Corp.") and
Schering-Plough, Ltd. ("Schering Ltd."), dated April 10, 1995, as amended to
date (the "Agreement") is entered into by and between the parties hereto with
reference to the facts below. Schering Corp. and Schering Ltd. are referred to
herein collectively as "Schering". Terms with initial capitals, which are not
specifically defined in this Addendum, shall have the defined meaning set forth
in the Agreement.

     WHEREAS, the Parties desire to modify the Agreement to provide for the
hiring of an additional field force by Millennium to be jointly funded by
Schering and Millennium.

     NOW, THEREFORE, in consideration of the foregoing premises and the mutual
covenants and obligations below, the Parties agree as follows:


1.0  DEFINITIONS

The following capitalized terms used in this Addendum, whether used in the
singular or plural, shall have the meanings set forth herein:

1.1  All references in the Agreement to "COR Therapeutics, Inc." and "COR" shall
hereinafter mean "Millennium Pharmaceuticals, Inc." and "Millennium",
respectively.

1.2  "ACTUAL 2003 A&P EXPENSES" shall have the meaning set forth in Section 3.4
of this Addendum.

1.3  "ADDITIONAL FIELD FORCE" shall mean the additional Sales Representatives
to be hired by Millennium to Co-Promote the Co-Promoted Products in the United
States pursuant to this Addendum, as well as the additional managers to be hired
by Millennium to manage such efforts.

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1.4  "ADDITIONAL FIELD FORCE EXPENSES" shall have the meaning set forth in
Section 3.1 of this Addendum.

1.5  "BUSINESS DEVELOPMENT COSTS" shall mean reasonable out-of-pocket costs
incurred by members of the Additional Field Force at regional and local levels
to address new business opportunities or implementation needs to support local
or regional sales objectives and overall business expansion.

1.6  "EXISTING 2003 BUDGET" shall have the meaning set forth in Section 3.4 of
this Addendum.

1.7  "MAXIMUM TRIAL COST" shall have the meaning set forth in Section 3.3 of
this Addendum.

1.8  "OBJECTIVES" shall have the meaning set forth in Section 2.4 of this
Addendum.

1.9  "REASONABLE SEVERANCE COSTS" shall mean reasonable and customary severance
and employment termination costs which in the aggregate do not exceed an amount
equal to one (1) months salary plus any accrued and unused vacation or sick
time.

1.10 "TERMINATION DATE" shall mean the date on which this Addendum expires, or
is terminated, in accordance with Section 4.1 or Section 4.2 of this Addendum,
respectively.

1.11 "TRIAL PERIOD" shall have the meaning set forth in Section 4.1 of this
Addendum.


2.0  HIRING AND MANAGEMENT OF THE ADDITIONAL FIELD FORCE

2.1  As of the Effective Date, Millennium commenced hiring up to a total of [**]
new employees (consisting of Sales Representatives and managers) that will be
members of the Additional Field Force. All Sales Representatives who are members
of the Additional Field Force shall be employees of Millennium and, except as
otherwise expressly set forth in this Addendum, shall be considered Millennium
Sales Representatives. Millennium shall be solely responsible for all aspects of
the hiring, management, supervision, compensation and performance of the
Additional Field Force.

2.2  Millennium shall maintain the Additional Field Force as a distinct and
separately identifiable field force from those of its other employees who
Co-Promote the Co-Promoted Products in the United States or who manage such
efforts. Millennium shall use commercially reasonable efforts to avoid
establishing or operating the Additional Field Force in a manner that reasonably
could be expected to engender dissatisfaction among Millennium's other Sales
Representatives (and their managers) who are Co-Promoting the Co-Promoted
Products in the United States, including, without limitation, setting the
salary, bonus and incentives of the Additional Field Force at an inappropriate
level as compared to Millennium's other Sales Representatives and managers.

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2.3  For purposes of clarity and avoidance of doubt, the Parties acknowledge and
agree that none of the members of the Additional Field Force are entitled to
participate in any of Schering's or its Affiliates' employee benefit plans,
including but not limited to the group health insurance plan, the
Schering-Plough Retirement Plan, the Schering-Plough Employees' 401K Savings
Plan, the Schering-Plough Employees' Profit-Sharing Incentive Plan, and the
Schering-Plough Stock Incentive Plan. Millennium further understands and agrees
that, if any Millennium employee who is a member of the Additional Field Force
is found to be a common law or statutory employee of Schering by (i) the
Internal Revenue Service; (ii) any other taxing authority; (iii) any regulatory
authority; or (iv) a court of law, then Millennium shall, and shall ensure that
its employees who are members of the Additional Field Force shall, hereby waive
any right of eligibility which might thereby accrue to Millennium or such
Millennium employees to participate in the aforesaid benefit plans of Schering
or its Affiliates.

2.4  The effectiveness of the Additional Field Force in Co-Promoting the
Co-Promoted Products will be periodically evaluated by the JSC using parameters
designed to provide an objective measurement of the benefits of investment in
the Additional Field Force (the "Objectives"), based upon information to be
obtained through a mutually agreeable structure and methodology incorporating
the use of a control group (at least during the Trial Period) and objective data
and information to be obtained by the Parties, including (i) sales of the
Co-Promoted Products in the United States, (ii) IMS audits, and/or (iii) data
and information obtained from other Third Party vendors. The first such
evaluation shall be conducted on or before February 15, 2004, and evaluations
shall thereafter be conducted within forty-five (45) days after the close of
each calendar quarter. Although evaluations will be conducted quarterly, the
test of whether the Objectives have or have not been met will be determined
based upon the performance of the Additional Field Force during the entire Trial
Period, or the then current renewal term, as measured by the then current
Objectives. The initial Objectives to apply during the Trial Period are set
forth in Exhibit A, attached hereto. The Objectives to apply during subsequent
periods will be revised and updated at least once annually, in a manner mutually
agreed by the Parties, with the first such update to establish the Objectives
for 2005 to be completed on or before November 30, 2004.


3.0  COST OF THE ADDITIONAL FIELD FORCE

3.1  Schering shall be responsible for reimbursing Millennium for [**] percent
([**]%) of the Additional Field Force Expenses (as defined below); PROVIDED,
HOWEVER, that such obligation shall be subject to the limitations set forth in
Sections 3.3 and 3.4 of this Addendum, and to any adjustments under Section 3.7
of this Addendum. "Additional Field Force Expenses" shall mean all costs
incurred by Millennium to establish, maintain and operate the Additional Field
Force, including, without limitation, reasonable recruiting costs, compensation
(salary, bonus, incentives, employee benefits and Reasonable Severance Costs),
reasonable and customary travel and entertainment costs, training costs, auto
costs, office equipment costs (such as laptops, printers, fax machines,
telephones, etc.) and Business Development Costs. Additional Field Force
Expenses shall not include any of the following that may be attributable to the
Additional Field Force: (i) capital expenditures (new facilities, etc.), (ii)
overhead (corporate expense allocations, etc.), (iii) severance or employment
termination payments in excess of Reasonable

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Severance Costs. In addition, the following types of Selling and Promotion
Expenses related to the Additional Field Force shall not be included in
Additional Field Force Expenses unless agreed to in writing in advance by
Schering and Millennium: costs of specialty sales forces (excluding the
Additional Field Force), consultants, home office personnel and other ancillary
services.

     3.1.1    To the extent that the termination of any employee who is a member
of the Additional Field Force involves severance or termination costs in excess
of Reasonable Severance Costs, Millennium will be solely responsible for any
such excess costs it may incur related to such termination, unless otherwise
agreed in writing in advance by the Parties through good faith discussions.

     3.1.2    For purposes of clarity and avoidance of doubt, the Parties
acknowledge and agree that none of the Selling and Promotion Expenses and, as of
July 1, 2003, none of the Business Development Costs, incurred by the Parties in
connection with any Sales Representatives that are not members of the Additional
Field Force and who Co-Promote the Co-Promoted Products in the United States are
Allowable Expenses under the Agreement, but rather that each Party bears its own
Selling and Promotion Expenses and, as of July 1, 2003, Business Development
Costs incurred in connection with such Sales Representatives who Co-Promote the
Co-Promoted Product.

3.2 Additional Field Force Expenses shall be reported quarterly by Millennium to
Schering in accordance with Section 9.4(a) of the Agreement. Subject to the
limitations set forth in Sections 3.3 and 3.4 of this Addendum, and any
adjustments under Section 3.7 of this Addendum, Schering shall reimburse
Millennium for [**] percent ([**]%) of such quarterly Additional Field Force
Expenses. Such reimbursement will be handled under Section 9.4(a) of the
Agreement by treating Schering's share of Additional Field Force Expenses as
Millennium's Allowable Expenses for the relevant calendar quarter for purposes
of determining the payments to be made by Schering to Millennium for such
quarter under Section 9.4(a).

3.3 The total of Additional Field Force Expenses for calendar year 2003 shall be
subject to the limitations set forth in Section 3.4. The total of Additional
Field Force Expenses for calendar year 2004 will not exceed [**] dollars ($[**])
(the "2004 Maximum Trial Cost"). Schering's obligation to reimburse Millennium
for Additional Field Force Expenses incurred during calendar year 2004 shall be
[**] the 2004 Maximum Trial Cost and Millennium shall be [**] during calendar
year 2004 [**] to the [**] by the parties [**] subject to such limitation.

3.4 The Parties acknowledge and agree that a total budget of [**] dollars
($[**]), in the aggregate, has already been established by the Parties for all
Advertising and Education Expenses and Business Development Costs to be incurred
by the Parties with respect to the Co-Promoted Products during calendar year
2003 (the "Existing 2003 Budget"). (The Existing 2003 Budget represents the JSC
approved budget for 2003 [**] dollars [**] during calendar year 2003, the
Parties [**] during calendar year 2003.) The Parties agree that Schering's share
of Additional Field Force Expenses for calendar year 2003 shall be included in
and subject to the Existing 2003 Budget. To the extent that the actual aggregate
total of Schering's share of

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Additional Field Force Expenses [**] by the Parties [**] the Existing 2003
Budget, [**] under this Addendum or the Agreement [**] for calendar year 2003
[**].

     3.4.1    The Parties have already agreed on the Additional Field Force
Expenses for calendar year 2004, as set forth in Section 3.3 of this Addendum,
and the JSC will separately agree on the 2004 Marketing Plan and Budget for
2004.

     3.4.2    With respect to calendar year 2005 and each subsequent year during
the term of this Addendum, the JSC will agree upon the annual budget for
Additional Field Force Expenses in connection with, and at the same time as, it
establishes the Marketing Plan and Budget for the same year under Section 5.4 of
the Agreement; provided that such budget shall be separate and distinct from the
Marketing Plan and Budget. Millennium shall [**] in 2005 or any subsequent
calendar year that [**] for such calendar year and Schering shall [**] to the
[**] in accordance with Section 4.4 of this Addendum.

3.5  The Parties acknowledge and agree that any Sales Representative Efforts
performed by the Additional Field Force in a given calendar year during the term
of this Addendum are separate from and in addition to each Party's individual
obligations to perform Sales Representative Efforts in the JSC approved
Marketing Plan and Budget for the United States for such calendar year. During
the term of this Addendum, any and all Sales Representative Efforts performed by
the Additional Field Force shall be excluded from the determination of each
Party's performance of its respective Sales Representative Efforts in the United
States under the JSC approved Marketing Plan and Budget for the relevant
calendar year, and shall not be used in any determination or adjustment to the
Sales Allocation between the Parties under Section 9.2 or 9.3 of the Agreement.

3.6  The first sentence of Section 10.3 of the Agreement is hereby amended and
restated to read in its entirety as follows:

     "Each Party shall keep or cause to be kept such records as are required to
     determine, in a manner consistent with generally accepted accounting
     principles in the United States, the sums or credits due under this
     Agreement, including but not limited to, Allowable Expenses, Development
     Costs, Pre-Marketing Expenses, Additional Field Force Expenses, Net Sales
     and Royalty-Bearing Sales. Such records shall include records of calls and
     other Sales Representative Efforts performed by the Additional Field Force
     that may be necessary to evaluate performance of the Additional Field Force
     against the Objectives pursuant to Section 2.4 of this Addendum."

3.7  Notwithstanding anything herein to the contrary, Schering's obligation to
reimburse Millennium for Additional Field Force Expenses shall be adjusted in
the event that the Additional Field Force is marketing and promoting one or more
products in the United States other than Co-Promoted Products. In such instance,
the percentage of the total Additional Field Force Expenses that Schering is
obligated to reimburse shall be proportionally reduced based upon the percentage
of time the Additional Field Force is marketing, promoting, detailing and
otherwise engaged in activities related to products other than Co-Promoted
Products. For example, if the Additional Field Force is devoting eighty percent
(80%) of its time to Co-

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Promoting the Co-Promoted Products in a given calendar quarter, then the
percentage of Additional Field Force Expenses for that quarter for which
Schering is responsible under Sections 3.1 and 3.2 of this Addendum shall be
reduced from [**] percent ([**]%) to [**] percent ([**]%).

4.0  TERMINATION OF FUNDING OBLIGATIONS

4.1  The Parties agree that this Addendum shall remain in effect, and the
Additional Field Force will be jointly funded, for a minimum period commencing
on the Effective Date and expiring on December 31, 2004 (the "Trial Period").
The term of this Addendum will thereafter be subject to annual one (1) year
renewals, as approved by the JSC in writing at least three (3) months prior to
the end of the Trial Period or the then current renewal term, based upon the
results of the evaluations performed under Section 2.4 of this Addendum. If the
JSC does not approve an annual renewal of the term of this Addendum, then this
Addendum shall expire at the end of the Trial Period or the then current renewal
term, as applicable.

4.2  Neither Party shall have the right to terminate this Addendum during the
Trial Period. In the event that the term of this Addendum is renewed under
Section 4.1, either Party shall have the right to terminate this Addendum during
such renewal term by providing written notice to the other Party in the event
that:

     (i)      The Additional Field Force is no longer engaged in activities to
              Co-Promote the Co-Promoted Products; or

     (ii)     The then current Objectives of the Additional Field Force have not
              been met, as reasonably determined by the JSC pursuant to Section
              2.4 of this Addendum; or

     (iii)    Millennium notifies Schering in writing that it no longer desires
              to maintain the Additional Field Force as a separate and distinct
              field force from its other Sales Representatives who Co-Promote
              the Co-Promoted Product in the United States.

Any termination under this Section 4.2 shall become effective upon the later of
(1) the last day of the then current calendar quarter, or (2) sixty (60) days
after the other Party's receipt of such written notice of termination.

4.3  Effective upon expiration of this Addendum pursuant to Section 4.1, or any
termination of this Addendum under Section 4.2, the rights and obligations of
the Parties under this Addendum shall terminate and, except as expressly set
forth in this Section 4.3, shall be of no further force or effect. The
provisions of the last sentence of Section 2.1, all of Sections 2.3, 3.6, 4.3
and 4.4, and Article V of this Addendum shall survive the expiration or
termination of this Addendum and remain in full force and effect. The Parties
further agree that the expiration or termination of this Addendum shall not
affect any rights or obligation of either Party that have accrued prior to the
Termination Date, including without limitation, Schering's obligation to
reimburse Millennium as described in Section 4.4 hereof, and for Schering's
share of any Additional Field Force Expenses accrued prior to the Termination
Date, including, without

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limitation, Additional Field Force compensation accrued, but not yet paid by
Millennium, prior to the Termination Date.

4.4  Notwithstanding anything in this Addendum or the Agreement to the contrary,
in the event that Millennium provides notice of termination of employment to one
or more of its employees who are members of the Additional Field Force, during
the sixty (60) day period following (i) a JSC decision not to approve renewal of
this Addendum or (ii) a notice of termination of this Addendum under Section
4.2, then any Reasonable Severance Costs incurred by Millennium related to the
termination of such employee(s) shall be deemed to be Additional Field Force
Expenses accrued prior to the Termination Date for purposes of Section 4.3
above. In the event that any such termination of a member of the Additional
Field Force involves any compensation or other costs in excess of Reasonable
Severance Costs, such excess costs shall be allocated between the Parties in
accordance with Section 3.1.1 of this Addendum.

5.0  MISCELLANEOUS

     A.       Each Party agrees to act in good faith and do all other acts as
may be necessary or appropriate in order to carry out the purposes and intent of
this Addendum.

     B.       This Addendum has been prepared jointly and shall not be strictly
construed against either Party.

     C.       The terms, conditions and existence of this Addendum shall be
treated by the Parties on a confidential basis, subject to Section 13.3 of the
Agreement and subject further to appropriate disclosure to employees, officers,
directors and shareholders of Schering-Plough Corporation (the corporate parent
of Schering) and its Affiliates, and/or Millennium, or as otherwise required by
law. Each of Schering and Millennium agrees to coordinate both the timing and
content of any public announcements relating to this Addendum and any such
public announcements shall be subject to the review and approval of the Parties
prior to public disclosure.

     D.       This Addendum to the extent set forth herein, amends, modifies and
supplements the Agreement. This Addendum, along with the Agreement, contains the
entire agreement between the Parties hereto with respect to the subject matter
set forth herein, and the terms of this Addendum are contractual and not a mere
recital. Except as expressly modified herein, all of the terms and provisions of
the Agreement shall remain in full force and effect and cannot be amended,
modified or changed in any way whatsoever except by a written instrument duly
executed by the Parties hereto.

     IN WITNESS WHEREOF, the Parties have executed this Addendum by their
authorized officers to be retroactively effective as of the Effective Date.

SCHERING CORPORATION               MILLENNIUM PHARMACEUTICALS,
                                   INC.

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By:      /s/Tasos Konidaris               By:      /s/ Arthur Hiller
   -----------------------------------       -----------------------------------

Title:   GVP, GPB Finance                 Title:   VP, Global Strategic Mkg.
      --------------------------------          --------------------------------

Date:    October 1, 2003                  Date:    October 1, 2003
     ---------------------------------         ---------------------------------

SCHERING-PLOUGH LTD.


By:      /s/Tasos Konidaris
   -----------------------------------

Title:   GVP, GDP Finance
      --------------------------------

Date:    October 1, 2003
     ---------------------------------

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EXHIBIT A

ADDITIONAL FIELD FORCE OBJECTIVES

-    [**]
     -  [**] in the United States [**]
     -  Accomplishment of this Objective will be [**] as agreed by the Parties).
     -  Results will be reported to the JSC.

-    [**]
     -  [**] the number of [**].
     -  [**] during [**]as measured [**]Results will be reported to the JSC

-    [**]
     -  [**] should demonstrate [**]. Accomplishment of this Objective will be
        [**].
     -  Results will be reported to the JSC.

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