Press Release

Seattle Genetics Expands Antibody-Drug Conjugate Collaboration with Genentech
Seattle Genetics to Receive $12 Million Upfront Payment, Over $900 Million in Potential Fees and Milestone Payments and Mid-Single Digit Royalties

BOTHELL, Wash., Aug 03, 2010 (BUSINESS WIRE) -- Seattle Genetics, Inc. (NASDAQ:SGEN) announced today that it has expanded its antibody-drug conjugate (ADC) collaboration agreement with Genentech, Inc., a member of the Roche Group (SWX:RO) (SWX:ROG) (Pink Sheets:RHHBY). Under the expanded agreement, Genentech will pay an upfront fee of $12 million for rights to utilize Seattle Genetics' ADC technology with additional antigens to be named by Genentech.

Genentech is responsible for research, preclinical and clinical development, manufacturing and commercialization of ADCs under the expanded agreement. Pursuant to the terms of the expansion, Seattle Genetics is eligible to receive more than $900 million in fees and milestones if all ADCs in the expanded portion of the collaboration are commercialized, as well as mid-single digit royalties on worldwide net sales of any resulting ADC products. Seattle Genetics is also eligible to receive annual maintenance fees and research support payments for potential assistance if requested by Genentech under the collaboration.

Seattle Genetics and Genentech established an initial ADC collaboration in 2002, under which Genentech has paid more than $30 million in collaboration payments. Under that agreement, Seattle Genetics is eligible to receive more than $500 million in milestone payments if all ADCs in the initial collaboration are commercialized, as well as mid-single digit royalties on worldwide net sales of any resulting ADC products.

"This expansion of our ADC collaboration with Genentech is another indication of the increasing value of our proprietary ADC technology," said Eric L. Dobmeier, Chief Business Officer of Seattle Genetics. "Our ongoing ADC collaboration with Genentech has resulted in multiple preclinical and clinical milestones, and we look forward to their continued progress with product candidates utilizing our ADC technology over the next several years."

"We are pleased to continue our ADC collaboration with Seattle Genetics. We believe ADCs will play an important role in the future of cancer therapy. Genentech is committed to exploring the therapeutic potential of ADCs in a variety of hematologic malignancies and solid tumors," said James Sabry, M.D., Ph.D., Vice President, Genentech Partnering.

ADCs are monoclonal antibodies that selectively deliver potent anti-cancer agents to tumor cells. With over a decade of experience and knowledge in ADC innovation, Seattle Genetics has developed proprietary technology employing synthetic, highly potent cell-killing agents called auristatins (such as MMAE and MMAF) and stable linker systems that attach auristatin to the antibody. Seattle Genetics' novel linker systems are designed to be stable in the bloodstream and release the potent cell-killing agent once inside targeted cancer cells. This approach is intended to spare non-targeted cells and thus reduce many of the toxic effects of traditional chemotherapy while enhancing the antitumor activity. Seattle Genetics has generated more than $130 million through its ADC technology license agreements with leading biotechnology and pharmaceutical companies.

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's lead product candidate, brentuximab vedotin (SGN-35), is in a pivotal trial under a Special Protocol Assessment with the U.S. Food and Drug Administration. Brentuximab vedotin is being developed in collaboration with Millennium: The Takeda Oncology Company. In addition, Seattle Genetics has five other clinical-stage programs: lintuzumab (SGN-33), dacetuzumab (SGN-40), SGN-70, SGN-75 and ASG-5ME. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Bayer, Celldex Therapeutics, Daiichi Sankyo, Genentech, GlaxoSmithKline, MedImmune, a subsidiary of AstraZeneca, Millennium: The Takeda Oncology Company and Progenics, as well as an ADC co-development agreement with Agensys, an affiliate of Astellas. More information can be found at http://www.seattlegenetics.com.

Certain of the statements made in this press release are forward looking. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Specifically, statements regarding the therapeutic potential of antibody-drug conjugates are forward looking and actual results may differ materially from these statements for various reasons. 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 our collaborators to perform their contractual obligations or advance products incorporating our technology. More information about the risks and uncertainties faced by Seattle Genetics is contained in the company's quarterly report on Form 10-Q for the quarter ended March 31, 2010 filed 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.

About Genentech

Founded more than 30 years ago, Genentech is a leading biotechnology company that discovers, develops, manufactures and commercializes medicines to treat patients with serious or life-threatening medical conditions. The company, a member of the Roche Group, has headquarters in South San Francisco, California. For additional information about the company, please visit http://www.gene.com.

SOURCE: Seattle Genetics, Inc.

Seattle Genetics, Inc.
Peggy Pinkston, 425-527-4160
ppinkston@seagen.com