EXHIBIT 10.2


         Addendum to Stock Exchange Agreement among Cytogen Corporation
         --------------------------------------------------------------
            and the Shareholders and Debtholders of Prostagen, Inc.
            -------------------------------------------------------


     WHEREAS,  on June 15, 1999, the parties entered a Stock Exchange  Agreement
among Cytogen  Corporation  and the  Shareholders  and Debtholders of Prostagen,
Inc. ( hereinafter, the "Stock Exchange Agreement"); and

     WHEREAS, pursuant to paragraph 1.6 of the Stock Exchange Agreement certain
additional consideration is due to the Shareho1ders and Debtholders of
Prostagen, Inc., i.e. Max Link, the Estate of S. Leslie Misrock, CC Consulting
A/S, Allan M. Fox (New Hope Holdings) and Misrock Holdings LP (hereinafter the
"Prostagen Partners"); and

     WHEREAS, certain disputes have arisen between Cytogen and the Prostagen
Partners regarding Cytogen's obligations under paragraph 1.6 of the Stock
Exchange Agreement; and

     WHEREAS, upon the death of S. Leslie Misrock, the Prostagen Partners have
selected Allan M. Fox to serve as Representative and granted him their
power-of-attorney to act in their stead in matters relating to this dispute; and

     WHEREAS,  the parties  hereto  wish to clarify the terms of their  original
agreement and resolve any disputes among them;

     WHEREFORE,  this  Addendum to the Stock  Exchange  Agreement is entered and
made effective this 14th day of May 2002 and provides as follows:

     1. In satisfaction of its obligations to Prostagen Partners under paragraph
1.6(a) and (c) of the


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Stock Exchange Agreement, Cytogen shall deliver to Representative a number of
Cytogen shares equal to $2 million divided by the Conversion Number (recomputed
as of the effective date of this Agreement). For purposes of this Agreement,
"Conversion Number" shall have the same meaning as in the Stock Exchange
Agreement. The shares shall be delivered in three equal tranches: the first
within three business days of the registration of stock pursuant to paragraph 5
infra; the second, 60 days and the third, 120 days following the effective date
of this Agreement. The Representative will provide instructions as to how such
shares shall be issued. Such shares shall be free of any and all restrictions
and shall be available for sale immediately upon delivery.

     2. In satisfaction of its obligations to Prostagen Partners under paragraph
1.6(b) and (d) of the Stock Exchange Agreement, Cytogen shall deliver to
Representative: (i) a number of Cytogen shares equal to $1 million divided by
the Conversion Number (recomputed as of the date of such delivery) on the
earlier of January 1, 2003 or the enrollment of the first patient by the PSMA
Development Company LLC (or any other entity with technology licensed from
Cytogen) in a Phase II clinical trial for immunotherapy for prostate cancer and
(ii) a number of Cytogen shares equal to $1 million divided by the Conversion
Number (recomputed as of the date of such delivery) on the earlier of July 1,
2003 or the enrollment of the first patient by the PSMA Development Company LLC
(or any other entity with technology licensed from Cytogen) in a Phase III
clinical trial for immunotherapy for prostate cancer. In the event that the
dates specified in subsections (i) and (ii) supra (i.e. January 1 and July 1,
2003) shall occur before the enrollments of the first patients in the Phase II
and III trials respectively, then the payment(s) shall be due on those dates
only if safety has been established in a completed Phase I clinical trial and
the research program on immunotherapy for prostate cancer is continuing on such
date(s). For the purposes
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of this paragraph, the research program shall be deemed to be "continuing,"
unless a public announcement has been made that the program has been terminated.
Notwithstanding the other provisions of this paragraph, the milestone payment
provided for in section (ii) shall be made no earlier than six months following
the payment under section (i). Cytogen shall provide Representative with
quarterly reports on the status of the immunotherapy research program. The
representative will provide instructions as to how such shares shall be issued.
Such shares shall be free of any and all restrictions and shall be available for
sale immediately upon delivery.

     3. In satisfaction of its obligations to Prostagen Partners under paragraph
1.6(e) of the Stock Exchange Agreement, Cytogen shall pay to Representative in
cash, amounts equal to 25% of net amounts received by Cytogen or any affiliated
entity pursuant to the PSMA Sublicense Agreement by and between Cytogen
Corporation and Northwest Biotherapeutics Inc., dated August 28, 2000 or any
amended or successor agreements relating to the same technology, in milestone
payments and/or royalties, after deduction of royalties payable by Cytogen to
Memorial Sloan-Kettering. Such payments shall be delivered to Representative
within 30 days of receipt by Cytogen. Cytogen shall provide Representative with
quarterly reports on the status of the Northwest Biotherapeutics' research
program. The Representative will provide instructions as to how such payments
shall be made. Representative shall be provided with reasonable access to the
books and records of Cytogen for the purpose of confirming the amounts of such
payments.

     4. In satisfaction of its obligations to Prostagen Partners under paragraph
1.6(f) of the Stock Exchange Agreement, Cytogen shall (i) within five days of
the effective date of this Agreement pay to Representative the sum of $60,000
and (ii) within three business days of the registration of stock pursuant to
paragraph 5 infra deliver to Representative 50,000 shares of Cytogen stock. The


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<PAGE>

Representative will provide instructions as to how such payment shall be made
and how such shares shall be issued. Such shares shall be free of any and all
restrictions and be available for sale immediately upon delivery.

     5. In further satisfaction of its obligations under the Stock Exchange
Agreement, Cytogen shall immediately undertake to register a sufficient number
of shares of its common stock to satisfy all of its obligations under this
Agreement and shall promptly release any remaining restrictions on the stock
distributed to Prostagen Partners at the time the Stock Exchange Agreement was
entered.

     6. Prostagen Partners shall assume liability for and indemnify Cytogen and
its officers and directors against any claims, judgments, costs and expenses
(including reasonable attorney's fees) made against it by Michael I. Sherman
arising under paragraph 3 of the Termination and Release of Employment Agreement
dated June 15, 1999 between Cytogen, Prostagen Inc. and Sherman.

     7. Prostagen Partners shall assume liability for and indemnify Cytogen and
its officers and directors against any claims, judgments, costs and expenses
(including reasonable attorney's fees) made against it by Gerard Klauer Mattison
& Co. or any of its successors or assigns arising from paragraphs 1 - 4 of this
Agreement.

     8. Except for such obligations as are set forth in this agreement,
Prostagen Partners hereby forever release and discharge Cytogen, its
officers and directors from any and all claims arising from or related to
the Stock Exchange Agreement.

     9. Except for such obligations as are set forth in this Agreement, Cytogen
hereby forever discharges and releases Prostagen Partners, collectively and
individually, from any and all claims arising from or related to the Stock
Exchange Agreement.


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     10. This Agreement constitutes the whole agreement among the parties with
respect to the issues addressed, supercedes all prior agreements and may be
amended only in writing signed by all parties.

     11. This Agreement is binding upon, and shall inure to the benefit of the
parties hereto, their respective agents, successors, assigns, representatives,
affiliates, partners, joint ventures, affiliates and parent and/or subsidiary
corporations.

     12. The parties agree that if any of the provisions of this Agreement were
not performed in accordance with their specific terms or were otherwise breached
that the parties shall be entitled to specific performance of the terms hereof,
in addition to any other remedy at law or equity.

     13. Each party hereto shall pay its own expenses incident to preparing for,
entering into and carrying out this Agreement.

     14. Except as otherwise required by law, neither party shall issue any
press releases or otherwise make any public statement with respect to the
transactions contemplated by this Agreement without prior consultation with the
other party.

     15. Cytogen's payment obligations under paragraphs 1 - 4 of this Agreement
shall be secured by amounts received by Cytogen or any affiliated entity
pursuant to the PSMA Sublicense Agreement by and between Cytogen Corporation and
Northwest Biotherapeutics Inc., dated August 28, 2000 or any amended or
successor agreements relating to the same technology, in milestone payments
and/or royalties, after deduction of royalties payable by Cytogen to Memorial
Sloan-Kettering and payments due to Prostagen Partners pursuant to paragraph 3
supra.. Cytogen hereby grants to Prostagen Partners a security interest in such
revenues.


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CYTOGEN CORPORATION                        PROSTAGEN PARTNERS


by:  /s/ H. Joseph Reiser                  by:  /s/ Allan M. Fox
     -----------------------                    -------------------------
     Dr. Joseph Reiser                          Allan M. Fox
     President and C.E.O.                       Representative









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                                 AMENDMENT NO. 1
                                       TO
                      ADDENDUM TO STOCK EXCHANGE AGREEMENT



         THIS AMENDMENT NO. 1 TO ADDENDUM TO STOCK EXCHANGE AGREEMENT AMONG
CYTOGEN CORPORATION AND THE SHAREHOLDERS AND DEBTHOLDERS OF PROSTAGEN, INC. (the
"Amendment") made effective as of the 13th day of August, 2002 (the "Effective
Date") by and among Cytogen Corporation, a Delaware corporation, with its
principal place of business at 600 College Road East, Princeton, New Jersey
08540 (the "Company") and the Shareholders and Debtholders of Prostagen, Inc.
(collectively, the "Prostagen Partners").


                                   WITNESSETH:

         WHEREAS, the Company and the Prostagen Partners are parties to that
certain Stock Exchange Agreement dated as of June 15, 1999 (the "Agreement");
and

         WHEREAS, the Company and the Prostagen Partners have clarified the
terms of the Agreement with an Addendum dated as of May 14, 2002 (the
"Addendum"); and

         WHEREAS, in compliance with securities law obligations, the Company
must issue any shares of common stock issuable to the Prostagen Partners
pursuant to the Agreement and the Addendum prior to the registration thereof;
and

         WHEREAS, the Company and the Prostagen Partners desire to amend the
Addendum to reflect the mutually agreed upon revised terms in accordance with
the provisions of this Amendment.

         NOW THEREFORE, in consideration of the premises and mutual covenants
contained herein, and intending to be legally bound hereby, the parties hereto
agree as follows:

         1.       Amendments.

          (a) The text of the third  sentence  ofP. 1 of the  Addendum  shall be
     revised in its entirety to read as follows:

         "The shares of Cytogen common stock to be delivered pursuant to this P.
1 shall be represented by one stock certificate for each recipient, and each
such stock certificate shall bear the following restrictive legends:



<PAGE>


              THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT
              OF 1933, AS AMENDED (THE "ACT"). NO SALE OR DISPOSITION OF THESE
              SECURITIES MAY BE AFFECTED WITHOUT THE PRIOR WRITTEN CONSENT OF
              THE COMPANY AND WITHOUT AN EFFECTIVE REGISTRATION STATEMENT
              RELATED THERETO OR AN OPINION OF COUNSEL SATISFACTORY TO THE
              COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE ACT.

              THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO LOCK-UP
              ARRANGEMENTS PURSUANT TO THAT CERTAIN ADDENDUM TO STOCK EXCHANGE
              AGREEMENT AMONG CYTOGEN CORPORATION AND THE SHAREHOLDERS AND
              DEBTHOLDERS OF PROSTAGEN, INC. DATED MAY 14, 2002, AS AMENDED."

          (b) The  following  text  shall  be  added  to the end  ofP.  1 of the
     Addendum:

         "The shares of Cytogen common stock to be issued pursuant to this P. 1
are subject to the following lock-up arrangements: (i) two-thirds of the shares
shall be transferable in accordance with all applicable federal and state
securities laws; and (ii) one-third of the shares shall not be transferred,
assigned, pledged, hypothecated, or otherwise disposed of prior to September 12,
2002, and thereafter only in accordance with all applicable federal and state
securities laws."

          (c) The text of P. 1, P. 2 and P. 4 shall be  amended  to delete  each
     occurrence of the following sentence in its entirety:

         "Such shares shall be free of any and all restrictions and shall be
available for sale immediately upon delivery."

          (d) The  following  text  shall  be  added  to the end  ofP.  2 of the
     Addendum:

         "In connection with its obligations under this P. 2, Cytogen hereby
agrees that on each date it reasonably determines that within thirty (30) days
of such date a payment will become due and payable to the Prostagen Partners,
Cytogen shall: (i) notify the Representative of the date on which Cytogen
believes such payment shall become due and payable; (ii) begin to prepare all
requisite filings and begin to take all actions reasonably required to effect
the registration of such shares to be so issued; and (iii) request from the
Representative such information as Cytogen deems necessary to effect the
registration of such shares. Cytogen further agrees to make any and all filings
required to be made by it in order to effect the registration of shares to be
issued pursuant to this P. 2 as soon as reasonably practicable after the
issuance of such shares."

          (e) The text of the first  sentence  ofP. 4 of the  Addendum  shall be
     revised in its entirety to read as follows:

         "In satisfaction of its obligations to the Prostagen Partners under P.
1.6(f) of the Stock Exchange Agreement, Cytogen shall (i) within five days of
the effective date of this Agreement pay to Representative the sum of $60,000
and (ii) within a reasonable time after the effective date of this Agreement,
deliver to Representative 50,000 shares of Cytogen stock. Each stock certificate
issued pursuant to this P. 4 shall bear the following restrictive legend:
<PAGE>

              THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT
              OF 1933, AS AMENDED (THE "ACT"). NO SALE OR DISPOSITION OF THESE
              SECURITIES MAY BE AFFECTED WITHOUT THE PRIOR WRITTEN CONSENT OF
              THE COMPANY AND WITHOUT AN EFFECTIVE REGISTRATION STATEMENT
              RELATED THERETO OR AN OPINION OF COUNSEL SATISFACTORY TO THE
              COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE ACT."

          (f) The full text of Section 5 of the Addendum shall be revised in its
     entirety to read as follows:

         "In further satisfaction of its obligations under the Stock Exchange
Agreement, Cytogen shall register those shares of its common stock issued to
satisfy its obligations under the Agreement as soon as reasonably practicable
after the issuance of such shares. Furthermore, Cytogen shall promptly release
any remaining restrictions on the stock distributed to the Prostagen Partners at
the time the Stock Exchange Agreement was entered."

         2.       Reference to and Effect on the Agreement.
                  ----------------------------------------

          (a)  On  and  after  the  Effective  Date,  each  reference  to  "this
     Addendum,"  "hereunder,"  "hereof," "herein," or words of like import shall
     mean and be a reference to the Addendum as amended hereby.  No reference to
     this  Amendment  need be made in any  instrument  or  document  at any time
     referring  to the  Addendum,  a  reference  to the  Addendum in any of such
     instrument  or document to be deemed to be a reference  to the  Addendum as
     amended hereby.

          (b) Except as expressly  amended by this Amendment,  the provisions of
     the Agreement and the Addendum shall remain in full force and effect.

         3.       Governing  Law.  This  Amendment  shall be governed by and
construed in accordance  with the laws of the State of New York.

         4.       Counterparts. This Amendment may be executed in one or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute a single instrument.

         5.       Effective  Date.  This  Amendment  shall be effective
immediately  upon execution by the Company and the Prostagen Partners.

                                   * * * * * *

<PAGE>


         IN WITNESS WHEREOF, the parties have executed and delivered this
Amendment as of the date first written above.

                                    CYTOGEN CORPORATION


                                    By:  /s/ H. Joseph Reiser
                                         --------------------------------------
                                         H. Joseph Reiser
                                         President and Chief Executive Officer


                                    PROSTAGEN PARTNERS


                                    By:  /s/ Alan M. Fox
                                         --------------------------------------
                                         Alan M. Fox
                                         Representative