Seattle Genetics Earns Milestone Payment from Initiation of SGN-40 Phase Ib Clinical Trial in Combination with Rituxan for Non-H

Seattle Genetics Earns Milestone Payment from Initiation of SGN-40 Phase Ib Clinical Trial in Combination with Rituxan for Non-Hodgkin Lymphoma

BOTHELL, Wash. -- Jan. 7, 2008--Seattle Genetics, announced today that it will receive a $4 million milestone payment from its collaborator Genentech, Inc. The milestone payment has been triggered by Genentech's initiation of a phase Ib clinical trial of SGN-40 in combination with Rituxan(R) (rituximab) for patients with relapsed follicular or marginal zone non-Hodgkin lymphoma.

"Preclinical data suggest that the combination of SGN-40 and Rituxan may have enhanced activity compared to either agent alone in multiple models of non-Hodgkin lymphoma, providing support for testing this combination in the clinical setting," said Thomas C. Reynolds, M.D., Ph.D., Chief Medical Officer of Seattle Genetics. "This trial is one of several being initiated under our collaboration with Genentech that will enable us to more fully evaluate the safety and therapeutic potential of SGN-40 for the treatment of hematologic malignancies such as non-Hodgkin lymphoma and multiple myeloma."

The phase Ib study will enroll patients with relapsed follicular or marginal zone non-Hodgkin lymphoma at multiple cancer centers in the U.S. The trial is designed to assess safety, pharmacokinetics and preliminary activity of escalating doses of SGN-40 when combined with Rituxan.

SGN-40 Development Program

SGN-40 is a humanized monoclonal antibody that is currently in phase I and phase II clinical trials for non-Hodgkin lymphoma and multiple myeloma under a worldwide collaboration agreement with Genentech. SGN-40 targets the CD40 antigen, which is expressed on most B lineage hematologic malignancies, as well as solid tumors such as bladder, renal and ovarian cancer.

In collaboration with Genentech, we are conducting a joint development plan for SGN-40 that includes six ongoing or planned clinical trials of SGN-40 both as a single agent and combined with standard therapies for non-Hodgkin lymphoma and multiple myeloma. A phase IIb clinical trial of SGN-40 in combination with R-ICE (Rituxan, ifosfamide, carboplatin and etoposide) in relapsed or refractory diffuse large B-cell lymphoma (DLBCL), a phase II single agent trial of SGN-40 in DLBCL and a phase Ib study of SGN-40 in combination with Revlimid(R) (lenalidomide) in relapsed or refractory multiple myeloma are ongoing.

Under the terms of the collaboration agreement, Seattle Genetics received an upfront payment of $60 million in February 2007, and is entitled to receive potential milestone payments exceeding $800 million and escalating double-digit royalties starting in the mid-teens on sales of SGN-40. Genentech funds research, development, manufacturing and commercialization expenses for SGN-40, including reimbursing Seattle Genetics for costs incurred in connection with activities it funds for the program.

About Non-Hodgkin Lymphoma

Non-Hodgkin lymphoma (NHL) represents a diverse group of cancers that develop in the lymphatic system and are characterized by uncontrolled growth and accumulation of abnormal lymphocytes. Lymphocytes are a type of white blood cells that are responsible for defending the body against infection. The most common forms of NHL are follicular and diffuse large B-cell lymphoma. According to the American Cancer Society, during 2007 approximately 63,200 cases of NHL were expected to be diagnosed in the United States and approximately 18,700 patients were expected to die from the disease.

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 to develop and commercialize SGN-40. Seattle Genetics also has two other lead clinical product candidates in ongoing clinical trials: SGN-33 and SGN-35. 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.

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. 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.