Exhibit 10.3

Confidential treatment has been requested for portions of this exhibit. The copy
filed herewith omits the information subject to the confidentiality request.
Omissions are designated as [***]. A complete version of this exhibit has been
filed separately with the Securities and Exchange Commission.

AMENDMENT No. 1

to

Collaboration and License Agreement

This AMENDMENT No. 1 to Collaboration and License Agreement (the “Amendment”),
effective as of May 15, 2008 (the “Amendment Date”), is entered into by and
between BAYER Healthcare AG, a German corporation, having its principal place of
business at D-51368, Leverkusen, Germany, (“Licensee”), and Seattle Genetics,
Inc., a Delaware corporation with an office at 21823 30th Drive S.E., Bothell,
WA 98021 (“Licensor”).

RECITALS

WHEREAS, BAYER Pharmaceuticals Corporation, an Affiliate of Licensee, and
Licensor entered into a Collaboration and License Agreement dated as of
September 27, 2004 (the “Collaboration Agreement”), which Collaboration
Agreement provides for the license to BAYER Pharmaceuticals Corporation of
Licensor technology useful for linking certain cytotoxins to other molecules,
such as antibodies; and

WHEREAS, BAYER Pharmaceuticals Corporation assigned the Collaboration Agreement
to Licensee as of letter dated January 8, 2007; and

WHEREAS, the initial Research Program Term under the Collaboration Agreement has
expired and Licensee now wishes to conduct further research work on additional
antibody-derived drug conjugates to the Designated Antigen (as defined in the
Collaboration Agreement), all of which shall be considered Licensed Products
according to the Collaboration Agreement, pursuant to a new research plan
attached hereto (the “New Research Plan”); and

WHEREAS, Licensor is willing to conduct such work under the New Research Plan
and renew the Research Program Term pursuant to the terms set forth herein;

NOW THEREFORE, in consideration of the mutual covenants set forth herein, the
Parties agree as follows (with all capitalized terms used but not defined herein
having the meanings set forth in the Collaboration Agreement):

[***] Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

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AGREEMENT

1. Definitions. The definition of Improvements set forth in Article 1 of the
Collaboration Agreement is hereby amended and restated in its entirety as set
forth below:

“Improvements” means all patentable or non-patentable inventions, discoveries,
modifications, variations, revisions or other know-how Controlled by either
Party after the Effective Date that utilize, incorporate, derive from, are made
using or are based on [***]; provided that Improvements shall not include [***]
or [***] covered by Section [***]. For purposes of clarification, Improvements
shall not include technology [***], either through internal development or
in-licensing, which relates to the methods or materials of linking cytotoxic
agents to molecules so long as such technology is [***] or otherwise based on or
derived from [***].

2. Term of the Research Program. The term of the Research Program shall be
renewed for a period of one (1) year from the Amendment Date (the “Renewed
Research Program Term”), unless terminated earlier in accordance with Article 13
of the Collaboration Agreement, upon payment to SGEN within thirty (30) days of
the Amendment Date of one million dollars ($1,000,000). Unless otherwise
specified herein and except for the ability to extend the Research Program Term
in Section 2.2, the terms set forth in the Collaboration Agreement relating to
Research Program Term apply to the Renewed Research Program Term.

3. New Research Plan. The New Research Plan attached hereto shall become
Schedule A-2 under the Collaboration Agreement and the Parties agree to use
Commercially Reasonable Efforts to perform, or cause to be performed, the
activities designated to each Party in such New Research Plan during the Renewed
Research Program Term. The New Research Plan set forth on Schedule A-2 shall be
considered a Research Plan pursuant to the Collaboration Agreement and all terms
and conditions set forth therein with regards to a Research Plan shall apply to
Schedule A-2. For clarification, the Parties agree and acknowledge that the
Research Plan set forth on Schedule A (the “Original Research Plan”) has been
completed and that neither Party shall have any further obligations with regards
to the activities set forth in the Original Research Plan during the Renewed
Research Program Term.

4. Research Fees. The FTE Fees as set forth in Section 6.1.2 of the
Collaboration Agreement shall be set at an [***] rate of [***] ($[***]) during
the Renewed Research Program Term. The Supply Fees as set forth in Section 6.1.2
shall be set at the rate of [***] percent ([***] %) of Licensor’s Cost of Goods.

[***] Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

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5. Schedule B. Schedule B to the Collaboration Agreement is hereby amended and
replaced with Schedule B attached hereto.

6. Miscellaneous.

 

  a. Except as expressly modified by this Amendment, the Collaboration Agreement
remains in full force and effect in accordance with the terms set forth therein.

 

  b. This Amendment shall be governed by and construed in accordance with the
laws of the State of New York, without regard to the conflict of law principles
thereof that may dictate application of the laws of any other state.

 

  c. This Amendment may be executed in two or more counterparts, each of which
shall be deemed an original, but all of which together shall constitute one and
the same instrument.

IN WITNESS WHEREOF, the parties have caused this Amendment to be executed by
their respective duly authorized officers as of the Amendment Date.

 

BAYER HEALTHCARE AG     SEATTLE GENETICS, INC. By:   /s/ PPA Wild     By:   /s/
Clay B. Siegall Name:   Dr. H. Wild     Name:   Clay B. Siegall Title:   SVP
GDD-L60     Title:   President & CEO By:   /s/ Dr. D. Linkenheil       Name:  
Dr. D. Linkenheil       Title:   Laws and Patents      

[***] Certain information on this page has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.