Press Release

Seattle Genetics Announces Antibody-Drug Conjugate Collaboration with Daiichi Sankyo

BOTHELL, Wash.--(BUSINESS WIRE)--July 8, 2008--Seattle Genetics, Inc. (Nasdaq:SGEN) announced today that it has entered into an exclusive, worldwide collaboration agreement with Daiichi Sankyo Co., Ltd. (TSE:4568) for the development of antibody-drug conjugates (ADCs) targeting a single antigen found on multiple types of solid tumors.

Under the terms of the collaboration, Seattle Genetics will receive an upfront payment of $4 million, progress-dependent milestone payments and mid-single digit royalties on worldwide net sales of resulting ADC products. Daiichi Sankyo is responsible for research, product development, manufacturing and commercialization of all ADC products under the collaboration. Seattle Genetics will receive material supply and annual maintenance fees as well as research support payments for assistance provided to Daiichi Sankyo in developing ADC products.

"This collaboration reflects the increasing value of our ADC technology to empower antibodies, and the growing evidence that ADCs can impact the way cancer is treated," said Eric L. Dobmeier, Chief Business Officer of Seattle Genetics. "The therapeutic potential of our ADC technology is being demonstrated through compelling clinical data with our lead internal ADC, SGN-35, as well as progress across our multiple ADC collaborations. We are pleased to be working with Daiichi Sankyo, one of the largest Japanese pharmaceutical companies and a global leader in oncology drug development."

ADCs utilize the targeting ability of monoclonal antibodies to deliver potent, cell-killing payloads to specific cells. Seattle Genetics has developed proprietary technology employing synthetic, highly potent drugs that can be attached to antibodies through proprietary linker systems. The linkers are designed to be stable in the bloodstream but to release the drug payload under specific conditions once inside target cells, thereby sparing non-target cells many of the toxic effects of traditional chemotherapy. To date, Seattle Genetics has generated more than $65 million through multiple ADC technology license agreements with leading biotechnology and pharmaceutical companies.

Seattle Genetics is advancing its own proprietary pipeline of ADC programs, including SGN-35, which is in two ongoing phase I clinical trials for patients with Hodgkin lymphoma and other CD30-positive hematologic malignancies. The company is also developing a number of preclinical ADC programs, including SGN-75 and an anti-CD19 ADC.

About Seattle Genetics

Seattle Genetics is a clinical stage biotechnology company focused on the development and commercialization of monoclonal antibody-based therapies for the treatment of cancer and autoimmune disease. The company has a worldwide collaboration with Genentech for SGN-40. Seattle Genetics also has two other product candidates in ongoing clinical trials: SGN-33 and SGN-35. In addition, the company has developed proprietary antibody-drug conjugate (ADC) technology comprising highly potent synthetic drugs and stable linkers for attaching the drugs to monoclonal antibodies. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech, Bayer, CuraGen, Progenics and MedImmune, a wholly-owned subsidiary of AstraZeneca, as well as an ADC co-development agreement with Agensys, a wholly-owned subsidiary of Astellas Pharma.

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential of products utilizing Seattle Genetics' ADC technology. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Factors that may cause such a difference include risks related to adverse clinical results as our product candidates move into and advance in clinical trials, risks inherent in early stage development and failure by Seattle Genetics to secure or maintain relationships with collaborators. More information about the risks and uncertainties faced by Seattle Genetics is contained in the Company's filings with the Securities and Exchange Commission. Seattle Genetics disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

CONTACT: Seattle Genetics Corporate Communications
Peggy Pinkston, 425-527-4160
ppinkston@seagen.com

SOURCE: Seattle Genetics, Inc.