<PAGE>   1

                                                                   EXHIBIT 10.28

                                                                ----------------
                                                                REDACTED VERSION
                                                                ----------------


                         [LETTER HEAD OF CR STRATEGIES]


                            MASTER SERVICE AGREEMENT

                                     BETWEEN

                   CR STRATEGIES, L.L.C. AND NEORX CORPORATION

                                FEBRUARY 28, 2001


<PAGE>   2

1.    OVERVIEW. This agreement states the terms and conditions by which CR
      Strategies, L.L.C. will deliver and NeoRx Corporation will receive any or
      all of the services provided by CR Strategies, L.L.C. The specific
      services to be provided hereunder are identified and described in detail
      in the applicable SERVICE LEVEL AGREEMENT attached to this Agreement. Each
      SERVICE LEVEL AGREEMENT accepted and executed by both parties is hereby
      incorporated by reference into this agreement. This agreement is intended
      to cover any and all services ordered by NeoRx Corporation and provided by
      CR Strategies, L.L.C.

2.    DEFINITIONS. When used in this Agreement, the "BOLDED" terms listed below
      shall have the following meanings:

(a)   "NEORX CORPORATION TECHNOLOGY" shall mean any proprietary technology owned
      by NeoRx Corporation, or licensed to NeoRx Corporation by third parties,
      and all similar proprietary information provided to CR Strategies, L.L.C.
      by NeoRx Corporation in connection with CR Strategies, L.L.C.'s provision
      of services to NeoRx Corporation.

(b)   "CONFIDENTIAL INFORMATION" shall mean any information disclosed by either
      party to the other party, directly or indirectly, in writing, orally or by
      inspection of tangible objects that is designated as "Confidential",
      "Proprietary" or some other similar designation, including information
      disclosed to a disclosing party by third parties. Confidential Information
      shall not include any information that: is or becomes publicly known and
      generally available without violation of this Agreement; is in the
      possession of the receiving party prior to the disclosure without the
      obligation to maintain its confidentiality; is independently developed by
      the receiving party without use of or reference to the disclosing party's
      Confidential Information; is obtained from third parties without
      restrictions on disclosure; or is required by law or legal process to be
      disclosed by the receiving party, provided that, if permitted, the
      receiving party gives the disclosing party prompt written notice prior to
      such disclosure.

(c)   "CR STRATEGIES, L.L.C. TECHNOLOGY" shall mean any designs, concepts,
      reports, documentation, written materials, and any techniques, methods,
      patterns, formulas and any and all intellectual property rights used,
      invented, developed or delivered by CR Strategies, L.L.C. in the course of
      providing services.

(d)   "EFFECTIVE DATE" shall mean the date on which authorized representatives
      of NeoRx Corporation and CR Strategies, L.L.C have executed this Master
      Service Agreement.


<PAGE>   3

3.    SERVICE LEVEL AGREEMENT. A SERVICE LEVEL AGREEMENT is attached to this
      Master Service Agreement. Extensions or modifications to such SERVICE
      LEVEL AGREEMENT may be requested by NeoRx Corporation subject to any
      procedures set forth in such SERVICE LEVEL AGREEMENT or herein, and shall
      be subject to CR Strategies, L.L.C.'s approval and execution of an
      amendment to the SERVICE LEVEL AGREEMENT or, if appropriate, a new SERVICE
      LEVEL AGREEMENT.

4.    PAYMENTS. NeoRx Corporation agrees to pay to CR Strategies, L.L.C.
      according to the schedule provided in the attached SERVICE LEVEL
      AGREEMENT.

      NeoRx Corporation shall remit payment to CR Strategies, L.L.C.,
      referencing the CR Strategies, L.L.C. invoice number, to:

               CR Strategies, L.L.C.
               21 Kimberly Court
               Collinsville, IL 62234

               Attn:  Accounts Receivable

      or to such other address as CR Strategies, L.L.C. shall designate in
      writing to NeoRx Corporation.

5.    OWNERSHIP AND LICENSE. The documentation, enhancements, revisions,
      updates, upgrades, modifications, and derivative works thereto, and all
      other items delivered by CR Strategies, L.L.C. under this Agreement are
      owned by NeoRx Corporation.

6.    CONFIDENTIAL INFORMATION. Each party agrees not to use any Confidential
      Information of the other party for any purpose except in the performance
      of the services. Each party agrees not to disclose any Confidential
      Information of the other party to such party's employees or to third
      parties, except those who need to know such information for the purposes
      hereof. Each party agrees that it shall take reasonable efforts to protect
      the secrecy of and avoid disclosure and unauthorized use of any
      Confidential Information of the other party. Without limiting the
      foregoing, each party shall take at least those measures that it takes to
      protect its most highly confidential information. All documents and other
      tangible objects containing or representing Confidential Information which
      have been disclosed by either party to the other party, and all copies
      thereof which are in the possession of the receiving party, shall be and
      remain the property of the disclosing party and shall promptly be returned


<PAGE>   4

      to the disclosing party upon the request of the disclosing party. Except
      as expressly provided herein, nothing contained in this Agreement is
      intended to grant any rights to either party under any patent, mask work
      right, copyright, trademark, service mark or other intellectual property
      right of the other party.

7.    LIMITED WARRANTY; LIMITATION OF LIABILITY.

      (a)   CR Strategies, L.L.C. warrants that the services shall materially
            comply with the specifications for such services set forth in the
            attached SERVICE LEVEL AGREEMENT. To the extent that any failure of
            the services to comply with the specifications results in a failure
            or inability of CR Strategies, L.L.C. to provide services to NeoRx
            Corporation, CR Strategies, L.L.C.'s obligations and liability with
            respect to such failure, and NeoRx Corporation's sole remedy with
            respect to such failure, will be limited to a refund of that portion
            of the SERVICE LEVEL AGREEMENT total cost that is attributable to
            the specific services giving rise to the claim for damages.

            Subject to the limitations set forth herein, NeoRx Corporation
            agrees to defend, indemnify and hold CR Strategies, L.L.C., and its
            officers, employees and agents harmless against and for all losses,
            causes of action, liability, costs, expenses, claims and damages,
            including all expenses of litigation, reasonable attorney's fees and
            court costs, that either party may at any time suffer or sustain or
            become liable for, due to injury or death of a person, or for damage
            to any property arising out of, in connection with, or incidental to
            the service(s) provided by CR Strategies, L.L.C. under the terms of
            this agreement.

      (b)   Except for NeoRx Corporation's payment obligations in section 4
            neither party shall be liable for any special, indirect, incidental
            or consequential damages (even if advised of the possibility of such
            damage), including without limitation, lost profits or lost savings,
            loss of use of services (except as specifically provided in the
            attached SERVICE LEVEL AGREEMENT), cost of capital, cost of
            substitute services or re-procurement, downtime costs, or damages
            resulting from loss of use of data or from third party claims. CR
            Strategies, L.L.C. shall have no liability from damages resulting
            from NeoRx Corporation's failure to perform their responsibilities
            hereunder, including, but not limited to, NeoRx Corporation's
            failure to provide accurate and complete information to CR
            Strategies, L.L.C. In no event, shall CR Strategies, L.L.C.'s
            liability for damages hereunder exceed the amounts paid to CR
            Strategies, L.L.C. by NeoRx Corporation for the services giving


<PAGE>   5

            rise to the claim for damages. NeoRx Corporation recognizes that the
            fees specified in the attached SERVICE LEVEL

      (c)   AGREEMENT are based in part on the limited warranty and limitation
            of liability set forth above. The remedies specified in this
            agreement are exclusive.

8.    WORKMANSHIP. CR Strategies, L.L.C. represents and warrants that all of the
      services specified in the attached SERVICE LEVEL AGREEMENT will be
      performed in a good, workmanlike and professional manner in accordance
      with industry standards by qualified persons fully familiar with the
      requirements for such services.

9.    FORCE MAJEURE. Except with respect to payment obligations, neither party
      shall be liable, nor shall any credit allowance or other remedy be
      extended, for any failure to fulfill its obligations under this Agreement
      due to causes beyond such party's reasonable control, including, but not
      limited to: acts of God, flood, extreme weather, fire or other natural
      calamity; any law, order, regulation, direction, action, or request of any
      governmental entity or any civil or military authority; unavailability of
      rights-of-way or materials; national emergencies, insurrections, riots, or
      wars; or strikes, lock-outs, work stoppages, or other labor difficulties.
      Each party agrees to notify the other party, as soon as possible, if such
      an event has occurred. The time for completion of any obligation to which
      this provision applies shall be extended for a period equivalent to the
      delay except for payment obligations, which shall be extended by a maximum
      of 10 days.

10.   INITIAL DISPUTE RESOLUTION. Except in the case of a dispute in which a
      party seeks injunctive relief or must file suit in order to avoid
      expiration of the applicable statute of limitations, all disputes shall be
      referred to the senior executives of the parties for resolution. If the
      dispute is not resolved within 60 days of receipt of the initiating
      party's written notice, or if the senior executives fail to discuss the
      dispute(s) within 30 days of receipt of the initiating party's notice,
      either party may pursue any and all remedies available at law.

11.   ASSIGNMENT. Either party may transfer its rights and duties under this
      Agreement to an entity which has acquired all of such party's capital
      stock or all or substantially all of such party's assets, provided that:
      (i) the acquiring entity is not a competitor of the other party, (ii) the
      acquiring entity agrees in writing to be bound by the terms of this
      Agreement, (iii) the acquiring entity is capable of meeting all of its
      obligations under this Agreement, (iv) the other party is in full
      compliance with its obligations under this Agreement, and (v) the other
      party consents in writing to such transfer in advance, which consent shall
      not be unreasonably withheld. In all other cases, neither this Agreement
      nor any rights or licenses granted


<PAGE>   6

      hereunder may be assigned, or duties delegated whether by operation of law
      or otherwise, by either party without the prior written consent of the
      other party. Any attempted assignment or delegation in violation of this
      Section shall be void and ineffective for all purposes. This Agreement
      shall be binding upon and inure to the benefit of NeoRx Corporation and
      any permitted assignee or successor of either party.

12.   TERM AND TERMINATION. This Agreement shall become effective on the
      Effective Date and shall remain in effect for the period specified in the
      attached SERVICE LEVEL AGREEMENT.

(a)   TERMINATION FOR MATERIAL BREACH.

(i)   In the event of any other material breach of this Agreement, the
      non-breaching party shall give the breaching party written notice
      describing such breach. In the event that the breaching party fails to
      cure such material breach within 30 days after receipt of written notice
      of such breach from the non-breaching party, the non-breaching party shall
      be entitled to terminate this Agreement upon written notice to the
      breaching party.

(ii)  Upon any termination of this Agreement for material breach by CR
      Strategies, L.L.C., NeoRx Corporation shall be entitled to a pro rata
      refund of amounts paid in advance for services.

(b)   INSOLVENCY. In the event either party shall (i) be declared bankrupt,
      become subject to any proceedings relating to its liquidation,
      reorganization, or insolvency, whether voluntary or involuntary, or for
      the appointment of a trustee or receiver or similar official, of or for it
      or any part of its property, or (ii) fail generally, or admit in writing
      its inability to pay its debts as they become due, or (iii) make a general
      assignment for the benefit of creditors, or (iv) be dissolved or otherwise
      cease business as an ongoing business entity, then the other party may,
      upon thirty (30) days prior written notice, terminate this Agreement for
      cause. In the event of the commencement of a case under the Bankruptcy
      Code by or against either party, and during the period prior to the entry
      of an order directing or authorizing the other party or its trustee in
      bankruptcy to assume, reject or otherwise terminate this Agreement, such
      party may exercise its rights under Bankruptcy Code Section 365(n), as
      such section may be amended or supplemented from time to time, and the
      exercise of such rights or resort to any remedies provided thereunder
      shall not be deemed the exclusive rights and/or remedies available to such
      party, but such party is entitled to obtain any relief to the fullest
      extent provided by applicable bankruptcy or nonbankruptcy law.


<PAGE>   7

(c)   RENEWAL AND EXPIRATION.

(i)   Apart from the above conditions the parties shall have the right to renew
      this Agreement upon mutual agreement, and it shall continue in effect for
      so long as there is a SERVICE LEVEL AGREEMENT in effect. Unless
      specifically provided otherwise, the term of a SERVICE LEVEL AGREEMENT,
      and NeoRx Corporation's right to use the services specified in such
      SERVICE LEVEL AGREEMENT, shall begin on the commencement date specified in
      Section 12 and continue in effect for the term stated in the SERVICE LEVEL
      AGREEMENT. Thereafter, the parties shall have the right to renew, upon
      mutual agreement, a SERVICE LEVEL AGREEMENT for successive renewal terms
      of duration equal to the original agreement.

(ii)  In the event of any expiration or termination of this Agreement NeoRx
      Corporation shall pay CR Strategies, L.L.C. on or before the effective
      date of termination all fees due, including but not limited to any out-of
      pocket expenses and reasonable travel and related expenses incurred up to
      the date of termination. Notwithstanding any termination or expiration of
      this Agreement, Sections 2, 4, 5, 6, 7, 8, 9, 10, 11, 12(c)(ii), 16, and
      17 shall survive termination.

13.   GOVERNING LAW. Interpretation, construction and enforcement of this
      Agreement shall be pursuant to the laws of Washington, U.S.A. The parties
      agree that the United Nations Convention for the International Sale of
      Goods shall not apply to this Agreement. Both parties agree to submit to
      the exclusive jurisdiction and venue of and agree that any cause of action
      arising under this Agreement shall be brought in a court in Washington.

14.   NOTICES. All notices required to be given under this Agreement shall be in
      writing and shall be deemed effective when received and shall be delivered
      in person, by facsimile, with a confirmation copy sent as provided herein,
      or by mail, postage prepaid, for delivery as registered or certified mail
      addressed, return receipt requested. All notices shall be deemed received
      (i) if given by hand, immediately, (ii) if given by registered mail, 3
      business days after posting, (iii) if given by express courier service,
      the next business day, or (iv) if given by facsimile, upon receipt thereof
      by the recipient's facsimile machine as indicated either in the sender's
      identification line produced by the recipient's facsimile machine or in
      the sender's transmission confirmation report as produced electronically
      by the sender's facsimile machine. Notices to CR Strategies, L.L.C. shall
      be sent to:


<PAGE>   8

            CR Strategies, L.L.C.
            605 Alder Street
            Prescott, AZ 86301

            Attn:  Raymond F. Schmelter, PhD, MBA

            FAX Number (520) 445-1378


      or, in the case of NeoRx Corporation, to:

            NeoRx Corporation
            410 West Harrison Street
            Seattle, WA 98119-4007

            Attn: Paul G. Abrams, M.D., J.D.

      or to such other address as either party may designate in writing to the
      other from time to time.

15.   ENTIRE AGREEMENT. This Agreement and the SERVICE LEVEL AGREEMENT
      referenced herein constitute the full and final expression of agreement
      between the parties with respect to the subject matter hereof and
      supersede all previous agreements and understandings, whether written or
      oral, relating to the subject matter hereof. This Agreement may not be
      altered, amended or modified except by written instrument signed by the
      duly authorized representatives of both parties. Any different, additional
      and/or pre-printed terms contained on purchase orders or other terms and
      conditions submitted by NeoRx Corporation shall be void. As used herein,
      "include" and its derivatives shall be deemed to mean, "including but not
      limited to".

16.   SEVERABILITY. Should any term of this Agreement, for any reason, be held
      to be illegal or unenforceable by a court of competent jurisdiction, the
      remaining terms of this Agreement will continue in full force and effect,
      and the offending term shall be limited or modified to the extent
      necessary to make it enforceable.

17.   GENERAL. (a) Either party may disclose that NeoRx Corporation has retained
      CR Strategies, L.L.C.'s services, and CR Strategies, L.L.C. may describe
      in general, non-confidential terms, CR Strategies, L.L.C.'s work under the
      Agreement in its marketing materials. Any other disclosure as to the
      nature of this Agreement or the work being performed hereunder shall be
      subject to the prior approval of both parties. (b) No waiver of or


<PAGE>   9

      failure to act regarding any breach of this Agreement shall constitute a
      waiver of any other breach. (c) Subject to applicable law, no action,
      other than an action for nonpayment, arising out of or relating to this
      Agreement may be brought by either party more than 2 years after the cause
      of action has accrued, provided that neither party shall be precluded from
      making a counterclaim or cross-claim in an action commenced by the other
      party or by a third party. CR Strategies, L.L.C.'s contractors may be
      direct and intended third party beneficiaries of this Agreement and may be
      entitled to enforce this Agreement directly against NeoRx Corporation to
      the extent that (i) this Agreement relates to the acquisition of CR
      Strategies, L.L.C. contractor's services, and (ii) CR Strategies, L.L.C.
      fails to enforce the terms of this Agreement on CR Strategies, L.L.C.
      contractors' behalf. This Agreement may be amended or modified only by a
      written instrument signed by an authorized representative of CR
      Strategies, L.L.C. and NeoRx Corporation.

      By the signatures of their duly authorized representatives below, CR
      Strategies, L.L.C. and NeoRx Corporation, intending to be legally bound,
      agree to all of the provisions of this Agreement.


ACCEPTED & AGREED TO:

CR Strategies, L.L.C.                     NeoRx Corporation

By:                                       By:

Adeoye Y. Olukotun, MD, MPH

Title: CEO                                Title:

Date: February 28, 2001                   Date:


By:

Raymond F. Schmelter, PhD, MBA

Title: President and COO

Date: February 28, 2001


<PAGE>   10

                      ATTACHMENT A. SERVICE LEVEL AGREEMENT

                                     BETWEEN

                   CR STRATEGIES, L.L.C. AND NEORX CORPORATION

                                FEBRUARY 28, 2001

                                    OVERVIEW

CR Strategies, L.L.C. will function as the Senior Management of Medical and
Regulatory Affairs for NeoRx Corporation through the end of December 2001 and
will perform the specific tasks listed under Section B below.

NeoRx Corporation and CR Strategies, L.L.C. have agreed that CR Strategies,
L.L.C. will endeavor to achieve the following objectives for this engagement:

-  Identify, propose, and build systems, processes and human resources
   internally at NeoRx Corporation toward establishing an NDA-ready
   organization.

-  Manage, through direct reporting and supervision, all Medical & Regulatory
   Affairs personnel. Mentor the STR program and its personnel through the term
   of the engagement.

            One of CR Strategies, L.L.C.'s principal members will be [*] for the
            duration of the engagement.

            CR Strategies, L.L.C. will report to Dr. Doug Given for the duration
            of the engagement.

[*] DESIGNATES PORTIONS OF THIS DOCUMENT THAT HAVE BEEN OMITTED PURSUANT TO A
REQUEST FOR CONFIDENTIAL TREATMENT FILED SEPARATELY WITH THE COMMISSION.

Services provided by CR Strategies, L.L.C. will commence on the date on which
NeoRx Corporation signs the Master Service Agreement to which this SERVICE LEVEL
AGREEMENT is attached and will terminate not later than December 31, 2001.

                                  WORK PRODUCT

CR Strategies, L.L.C. will perform the following specific tasks for NeoRx
Corporation:

-  Identify and procure, according to the terms in Section D below, a complete
   problem-solving team to manage the STR clinical and regulatory program.


<PAGE>   11

-  Form [*] capable of crossing the threshold acceptable to FDA. All consulting
   costs for these experts will be billed by the consultants directly to NeoRx
   Corporation.

-  Prepare for [*] with FDA.

-  Develop [*] acceptable to FDA.

-  Identify and set up clinical sites appropriate to performing [*].

-  Manage the performance of the [*] clinical study.

-  Analyze, submit to FDA, and defend clinical data developed in [*].

-  Develop a protocol for performing [*] for a subsequent [*] clinical trial.

-  Initiate the [*] clinical trial.

-  Manage the relationship with PPD Contract Research Organization.

-  Perform potential problem analysis and develop a plan to manage regulatory
   risk.

-  Develop internal NeoRx systems to prepare for NDA submission.

-  Assist in identifying, recruiting, and training NeoRx human resources to
   complete the [*] clinical trial and submit the NDA.

NeoRx Corporation will provide CR Strategies, L.L.C. with full access to its STR
project employees, subcontractors, and consultants, and all necessary STR
project data and documentation to allow CR Strategies, L.L.C. to fulfill its
obligations under this SERVICE LEVEL AGREEMENT.

             MATERIALS, SHIPPING, TRAVEL, SITE VISITS, PHOTOCOPYING

Expenses incurred by CR Strategies, L.L.C. in providing these services are
anticipated to not exceed approximately 20% of the price of this SERVICE LEVEL
AGREEMENT and will be separately billed to NeoRx Corporation on a bi-weekly
basis. If for any reason prices exceed 20% of the price of this SERVICE LEVEL
AGREEMENT, CR Strategies, L.L.C. will obtain NeoRX Corporation's approval prior
to proceeding. Expected costs include, but are not limited to, travel, travel
expenses (meals and lodging), telephone, fax, courier, shipping costs, copying,
materials, etc. When either party to this agreement deems travel necessary, CR
Strategies, L.L.C. will contact NeoRx Corporation to reach agreement about costs
and trip duration.

                          PRICING AND PAYMENT SCHEDULE

CR Strategies, L.L.C. will perform the tasks indicated in Section B for [*],
plus [*] stock options ([*] for each CR Strategies, L.L.C. principal member),
plus expenses as described in Section C. The cost breakdown for the engagement
is as follows:

<TABLE>
<CAPTION>
<S>                                 <C>
CR Strategies Salaries              [*]
Administrative Overhead (25%)       [*]
            Total                   [*]
</TABLE>

One hundred percent of Administrative Overhead [*] will be invoiced immediately
upon commencement of the engagement. [*] of the CR Strategies, L.L.C. salaries
shown above ([*]) will be invoiced at the end of each calendar quarter,
commencing March 30, 2001. In addition, it is anticipated that the following
professionals will subcontract directly with NeoRx, but be managed by CR
Strategies, L.L.C., for approximately the following salaries in order to further
the objectives listed in Section A:


<PAGE>   12

<TABLE>
<CAPTION>
      --------------------------------------------------------------------------
                                       Fully-
      Position                         Loaded
                                     Annualized  Hours/  Hourly  Weeks/ 10-Month
                                       Salary     Week    Rate    Year   Total
      --------------------------------------------------------------------------
<S>                                  <C>         <C>     <C>     <C>     <C>
      Ph.D. Regulatory Director           [*]     [*]     [*]     [*]     [*]
      MD Safety Reviewer                  [*]     [*]     [*]     [*]     [*]
      M.S. Statistician                   [*]     [*]     [*]     [*]     [*]
      M.S. Senior CRA                     [*]     [*]     [*]     [*]     [*]
      B.S. Senior CRA Safety Reviewer     [*]     [*]     [*]     [*]     [*]
      B.S. Regulatory Specialist          [*]     [*]     [*]     [*]     [*]
      B.S. Medical Writer                 [*]     [*]     [*]     [*]     [*]
      --------------------------------------------------------------------------
                                                         Total            [*]
      --------------------------------------------------------------------------
</TABLE>

CR Strategies, L.L.C. will invoice NeoRx Corporation a one-time charge of 10% of
the 10-month salary for each of these, or other similar, professionals that CR
Strategies, L.L.C. successfully recruits as subcontractors to the STR project.

The price in this quotation is valid for 30 days from the date on the cover
sheet of this SERVICE LEVEL AGREEMENT.