Seattle Genetics Initiates Phase II Clinical Trial of SGN-40 for the Treatment of Non-Hodgkin's Lymphoma.

BOTHELL, Wash. -- Seattle Genetics, Inc. (Nasdaq: SGEN) announced today that the company has initiated a phase II clinical trial of SGN-40 for the treatment of patients with diffuse large B-cell lymphoma, the most common type of aggressive non-Hodgkin's lymphoma (NHL).

Positive phase I data were reported last week at the American Society of Hematology annual meeting demonstrating that SGN-40 is well-tolerated and induces objective antitumor activity in patients with relapsed or refractory NHL. Out of 31 evaluable patients, five (16%) had measurable objective responses, including one complete response ongoing after 41 weeks. Four patients achieved partial responses, three of which remain durable at 10, 18 and 31 weeks. Three of the five responses were in patients with diffuse large B-cell lymphoma. Eight additional patients (26%) had stable disease at the end of treatment. SGN-40 was well-tolerated using a dose-loading schedule and no dose-limiting toxicity or immunogenicity was identified.

"Advancing SGN-40 into mid-stage clinical trials is a significant milestone for Seattle Genetics," said Clay B. Siegall, Ph.D., President and Chief Executive Officer of Seattle Genetics. "Relapsed and refractory aggressive NHL represents an important market opportunity for SGN-40 because currently available treatment options inadequately address the needs of this patient population."

The single-agent phase II study is designed to assess the antitumor activity, tolerability and pharmacokinetic profile of SGN-40 in patients with relapsed or refractory diffuse large B-cell lymphoma. The trial is expected to enroll up to 40 patients at multiple centers in the United States.

In addition to the diffuse large B-cell lymphoma study, SGN-40 is in phase I clinical trials for relapsed/refractory multiple myeloma and chronic lymphocytic leukemia. The company is also planning combination studies in NHL and multiple myeloma to begin in 2007.

About SGN-40

SGN-40 is a humanized monoclonal antibody that targets the CD40 antigen, which is highly 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, and may also play a role in immunologic diseases.

About Diffuse Large B-Cell Lymphoma

Non-Hodgkin's lymphoma represents a diverse group of cancers that develop in the lymphatic system. When lymphocytes, or white blood cells, which are responsible for defending the body against infection, divide and multiply uncontrollably, malignant tumors can form. The American Cancer Society estimates that more than 58,000 people will be diagnosed with NHL in the United States in 2006 and approximately 19,000 will die from the disease. Diffuse large B-cell lymphoma is an aggressive subtype of NHL, representing approximately 70% of all newly diagnosed cases of aggressive disease.

About Seattle Genetics

Seattle Genetics is a biotechnology company developing monoclonal antibody-based therapies for the treatment of multiple types of cancer, including non-Hodgkin's lymphoma, multiple myeloma, acute myeloid leukemia and Hodgkin's disease. The company has also 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 currently has license agreements for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech, Bayer, CuraGen and MedImmune. 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. 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 II clinical trial and the risk of adverse clinical results as SGN-40 moves into and 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.