* ] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY BRACKETS, HAS BEEN OMITTED BECAUSE IT IS BOTH (I) NOT MATERIAL AND (II) IS THE TYPE THAT THE REGISTRANT TREATS AS PRIVATE OR CONFIDENTIAL. 2 pursuant to Attachment 1 hereto,...

[ * ] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY BRACKETS, HAS BEEN OMITTED BECAUSE IT IS BOTH (I) NOT MATERIAL AND (II) IS THE TYPE THAT THE REGISTRANT TREATS AS PRIVATE OR CONFIDENTIAL. Exhibit 10.3 FIRST AMENDMENT TO DEVELOPMENT AND SUPPLY AGREEMENT Effective as of date of the last signature below, Xxxxxx Laboratories, an Illinois corporation having a principal place of business at 000 Xxxxxx Xxxx Xxxx, Xxxxxx Xxxx, Xxxxxxxx 00000-0000 (“Abbott”), and Seattle Genetics, Inc., a Delaware corporation having a principal place of business at 00000 – 00xx Xxxxx Xxxxxxxxx xx Xxxxxxx, Xxxxxxxxxx 00000 (“Seattle Genetics”) (individually the “Party” or collectively the “Parties”) agree to the following terms and conditions ("First Amendment") as set forth below. WHEREAS, the Parties entered into a Development and Supply Agreement with an Effective Date of February 23, 2004 for the manufacture of a chimeric anti-CD30 AC10 monoclonal antibody known as SGN-30, which also constitutes the antibody component of SGN-35 (the “Agreement”); and WHEREAS, the Parties have agreed to conduct additional development and manufacturing work pursuant to the terms and conditions of the Agreement; and NOW, THEREFORE, in consideration of the mutual covenants and agreements contained here and for other good and valuable consideration, the receipt and sufficiency of which is hereby acknowledged, the Parties agree as follows: 1. Incorporation of the Agreement. All capitalized terms which are used but not otherwise defined herein shall have the same meanings as set forth in the Agreement, and the Agreement, to the extent not inconsistent with this First Amendment, is incorporated herein by this reference as though the same was set forth in its entirety. To the extent any terms and provisions of the Agreement are inconsistent with the amendments set forth in Paragraph 2 below, such terms and provisions shall be deemed superseded hereby. Except as specifically set forth herein, the Agreement shall remain in full force and effect and its provisions shall be binding on the parties hereto. 2. Process Development Work. The Parties agree that Abbott shall perform the activities set forth in Stages 1, 2 and 4 of Attachment 1 hereto pursuant to the terms and conditions of the Agreement. 3. Additional Clinical Supplies. The Parties agree that Abbott shall manufacture and Seattle Genetics shall purchase [*] of clinical Bulk Drug Substance as described in Stage 3 of Attachment 1 hereto in accordance with the terms and conditions of the Agreement, including the Bulk Drug Substance Specifications set forth therein; provided that the total price for all [*] shall be $[*]excluding raw material costs. Abbott shall initiate billing and will continue in accordance with the Payment Schedule attached hereto and Seattle Genetics shall be responsible for payment of Stage 3 in full [*]. Stage 3 xxxxxxxx may be combined on the same invoice with other, regular Payment Schedule charges. Abbott shall reserve capacity for these [*]in Xxxxxx’x [*] facility beginning on or before [*]. 4. Payment Schedule. As compensation for the activities to be performed by Abbott

[ * ] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY BRACKETS, HAS BEEN OMITTED BECAUSE IT IS BOTH (I) NOT MATERIAL AND (II) IS THE TYPE THAT THE REGISTRANT TREATS AS PRIVATE OR CONFIDENTIAL. 2 pursuant to Attachment 1 hereto, Seattle Genetics shall pay to Abbott the fees set forth in Attachment 2, on the dates specified therein. 5. Project References. All references to the Project set forth in the Agreement, with the exception of the Payment Schedule and Facility Reservation Fee for the Project, shall also be deemed to apply to the activities performed by Abbott, pursuant to this First Amendment. 6. Termination Fee. The termination fee set forth in Section 7.1 of the Agreement shall hereby be [*] from $[*] to $[*] 7. Effectuation. The amendment to the Agreement contemplated by this First Amendment shall be deemed effective as of the last date written below upon the full execution of this First Amendment and without any further action required by the parties hereto. There are no conditions precedent or subsequent to the effectiveness of this First Amendment. All terms and conditions set forth in Agreement that are not amended hereby shall remain in full force and effect. Any term of this First Amendment may be amended with the written consent of both parties. From the date hereof, any reference to the Agreement shall be deemed to refer to the Agreement as amended by this First Amendment. 8. Counterparts. This First Amendment may be executed in two or more counterparts, each of which shall be deemed to be an original, but all of which together shall constitute one and the same instrument. One or more counterparts of this First Amendment may be delivered by facsimile, with the intention that delivery by such means shall have the same effect as delivery of an original counterpart thereof. 9. Entire Agreement. This First Amendment and exhibits hereto are the product of both of the parties hereto, and together with the Agreement and exhibits thereto constitute the entire agreement between such parties pertaining to the subject matter hereof, and merge all prior negotiations and drafts of the parties with regard to the transactions contemplated herein. IN WITNESS WHEREOF, the parties have executed this First Amendment as of the date last set forth below. XXXXXX LABORATORIES SEATTLE GENETICS, INC. By: /s/ Xxxx X. XxXxxxxx By: /s/ Xxxx X. Xxxxxxx Name: Xxxx X. XxXxxxxx Name: Xxxx X. Xxxxxxx Title: GM, Commercial Operations Title: President & CEO Date: April 17, 2008 Date: April 17, 2008

[ * ] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY BRACKETS, HAS BEEN OMITTED BECAUSE IT IS BOTH (I) NOT MATERIAL AND (II) IS THE TYPE THAT THE REGISTRANT TREATS AS PRIVATE OR CONFIDENTIAL. ATTACHMENT 1 [*]

[ * ] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY BRACKETS, HAS BEEN OMITTED BECAUSE IT IS BOTH (I) NOT MATERIAL AND (II) IS THE TYPE THAT THE REGISTRANT TREATS AS PRIVATE OR CONFIDENTIAL. ATTACHMENT 2 PAYMENT SCHEDULE [*]