Seattle Genetics Achieves Milestones as Genentech Advances Two Antibody-Drug Conjugates (ADCs) into Phase II Development

Seattle Genetics Achieves Milestones as Genentech Advances Two Antibody-Drug Conjugates (ADCs) into Phase II Development

Seattle Genetics, Inc.Investors:Peggy Pinkston, 425-527-4160orMedia:Tricia Larson, 425-527-4180

(NASDAQ:SGEN) announced today that it will receive undisclosed milestone payments under its antibody-drug conjugate (ADC) collaboration with Genentech, a member of the Roche Group (SWX:RO) (SWX:ROG) (OTCQX:RHHBY). The milestones were triggered by Genentech’s advancement of two ADCs utilizing Seattle Genetics technology into phase II clinical development. The phase II randomized, open-label study is designed to evaluate the safety and efficacy of ADCs anti-CD22 (DCDT2980S, RG7593) and DCDS4501A (RG7596) each in combination with Rituxan® (rituximab) in patients with relapsed or refractory follicular non-Hodgkin lymphoma and relapsed or refractory diffuse large B-cell lymphoma.

“Progress by our ADC collaborators, notably Genentech entering phase II clinical development, highlight the continued promise of ADCs for the treatment of cancer and further support Seattle Genetics’ leadership position in the field,” said Clay B. Siegall, Ph.D., President and Chief Executive Officer of Seattle Genetics. “Across our internal and collaborator programs, there are more than 15 ADCs in clinical development utilizing our technology, spanning a range of both hematologic malignancies and solid tumors.”

Under the ADC collaboration agreement, Genentech has rights to use Seattle Genetics’ ADC technology with antibodies against targets selected by Genentech. Genentech is responsible for research, product development, manufacturing and commercialization activities under the collaboration. Seattle Genetics is entitled to receive fees, progress-dependent milestone payments and royalties on net sales of any resulting ADC products.

ADCs are monoclonal antibodies that are designed to selectively deliver cytotoxic agents to tumor cells. With over a decade of experience and knowledge in ADC innovation, Seattle Genetics has developed proprietary technology employing synthetic cytotoxic agents, such as monomethyl auristatin E (MMAE) and monomethyl auristatin F (MMAF), and stable linker systems that attach these cytotoxic agents to the antibody. Seattle Genetics’ 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 antitumor activity.

Seattle Genetics is a biotechnology company focused on the development and commercialization of monoclonal antibody-based therapies for the treatment of cancer. The U.S. Food and Drug Administration granted accelerated approval of ADCETRIS in August 2011 for two indications. ADCETRIS is being developed in collaboration with Millennium: The Takeda Oncology Company. In addition, Seattle Genetics has three other clinical-stage ADC programs: SGN-75, ASG-5ME and ASG-22ME. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Abbott, Agensys (an affiliate of Astellas), Bayer, Celldex Therapeutics, Daiichi Sankyo, Genentech, GlaxoSmithKline, Millennium, Pfizer and Progenics, as well as ADC co-development agreements with Agensys and Genmab. More information can be found at .

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential of Seattle Genetics’ ADC technology and development plans for its ADC product candidates and its collaborators’ product candidates. 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 the inability to show sufficient safety or activity as our or our collaborators’ ADC product candidates move into and advance in clinical trials. 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 June 30, 2012, 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.