Trial Initiation Triggers $4 Million Milestone Payment from Genentech

BOTHELL, WA, USA | November 1, 2007 | Seattle Genetics, Inc. (Nasdaq:SGEN) announced today that it has initiated a phase Ib clinical trial of SGN-40 in combination with Revlimid(R) (lenalidomide) and dexamethasone, a steroid, for patients with relapsed or refractory multiple myeloma. As a result, the company will receive a $4 million milestone payment from its collaborator Genentech, Inc.

"Despite therapeutic advances over the past several years, multiple myeloma remains an incurable disease and significant unmet medical need," said Thomas C. Reynolds, M.D., Ph.D., Chief Medical Officer of Seattle Genetics. "There is no antibody therapeutic approved for the treatment of multiple myeloma. Based on encouraging preclinical data, we are moving forward with this phase Ib study to evaluate the safety and activity of Revlimid combined with SGN-40 in patients with multiple myeloma."

Approximately 68,000 people in the U.S. have multiple myeloma and, according to the American Cancer Society, about 20,000 new cases will be diagnosed during 2007.

The phase Ib, open-label single-arm clinical trial is expected to enroll up to approximately 40 relapsed or refractory multiple myeloma patients at multiple sites in the United States. Patients will receive escalating doses of SGN-40 in combination with Revlimid and dexamethasone. The study will assess safety and tolerability of the combination, preliminary activity data and pharmacokinetics.

SGN-40 Development Program
SGN-40 is a humanized monoclonal antibody that targets the CD40 antigen, which is expressed on most B lineage hematologic malignancies including non-Hodgkin’s lymphoma, multiple myeloma and chronic lymphocytic leukemia. CD40 is also found on many types of solid tumors, including bladder, renal and ovarian cancer.

Under the terms of an exclusive worldwide collaboration agreement for the development and commercialization of SGN-40, Seattle Genetics and Genentech are executing on a broad development plan that includes initiating five phase Ib-IIb clinical trials in combination with standard regimens for both multiple myeloma and non-Hodgkin’s lymphoma by early 2008, as well as advancing an ongoing phase II single-agent clinical trial in diffuse large B-cell lymphoma.

Seattle Genetics received an upfront payment of $60 million in February 2007, and has the potential to receive milestone payments exceeding $800 million and escalating double-digit royalties starting in the mid-teens. In addition, Genentech funds research, development, manufacturing and commercialization costs, including reimbursing Seattle Genetics for its costs to conduct SGN-40 clinical trials and development activities.

About Multiple Myeloma
Multiple myeloma is a cancer of plasma cells, a type of white blood cell found primarily in the bone marrow. In multiple myeloma, malignant plasma cells grow continuously, destroying normal bone tissue and crowding out normal blood cell production. Multiple myeloma is an incurable disease in which patients can experience symptoms that significantly impact their quality of life, including pain, anemia, fatigue, recurrent infection and kidney failure. This year, nearly 11,000 Americans will die from the disease.

About Seattle Genetics
Seattle Genetics is a biotechnology company developing monoclonal antibody-based therapies for the treatment of multiple types of cancer, including lymphoma, multiple myeloma, leukemia and solid tumors. The company has an exclusive worldwide collaboration agreement with Genentech to develop and commercialize SGN-40. Seattle Genetics also has three other proprietary programs in ongoing clinical trials: SGN-33, SGN-35 and SGN-30. In addition, the company has developed proprietary antibody-drug conjugate (ADC) technology comprised of 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, as well as an ADC co-development agreement with Agensys. More information can be found at www.seattlegenetics.com.

Certain of the statements made in this press release are forward-looking, such as those, among others, relating to the therapeutic potential of SGN-40 in combination or as a single-agent. 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 in this phase I clinical trial and the risk of adverse clinical results as SGN-40 advances in clinical trials. 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.

SOURCE: Seattle Genetics, Inc.