Seattle Genetics to Present Brentuximab Vedotin and Dacetuzumab Data at the 51st American Society of Hematology Annual Meeting and Exposition

Seattle Genetics, Inc. (Nasdaq: SGEN) today announced that data from its brentuximab vedotin (SGN-35) and dacetuzumab (SGN-40) programs will be reported at the upcoming 51^st American Society of Hematology (ASH) 2009 Meeting and Exposition being held December 5-8, 2009 in New Orleans, Louisiana. A summary of the company’s ASH presentations is below and full abstracts can be accessed at the ASH website at www.hematology.org.

Brentuximab vedotin data:

The antibody-drug conjugate brentuximab vedotin (SGN-35) induced multiple objective responses in patients with relapsed or refractory CD30-positive lymphomas in a phase 1 weekly dosing study

• Sunday, December 6, 2009, 6:00 p.m. - 8:00 p.m. Central Time (CT)
• Abstract # 2731 (poster board # II-707)
• First author: Dr. Michelle Fanale, MD Anderson Cancer Center, University of Texas, Houston, Texas

Dacetuzumab data:

Dacetuzumab (SGN-40), lenalidomide, and weekly dexamethasone in relapsed or refractory multiple myeloma: multiple responses observed in a phase 1b study

• Sunday, December 6, 2009, 6:00 p.m. - 8:00 p.m. CT
• Abstract # 2870 (poster board # II-846)
• First author: Dr. Edward Agura, Baylor Sammons Cancer Center, Dallas, Texas

CD40 pathway activation status predicts response to CD40 targeted therapy in diffuse large B-cell lymphoma

• Sunday, December 6, 2009, 6:00 p.m. - 8:00 p.m. CT
• Abstract # 2721 (poster board # II-697)
• First author: David Dornan, Ph.D., Genentech, Inc.

A phase 1b clinical trial of dacetuzumab in combination with rituximab and gemcitabine: multiple responses observed in patients with relapsed diffuse large B-cell lymphoma

• Monday, December 7, 2009, 3:30 p.m. CT
• Abstract # 586
• Oral presentation in rooms R02-R05
• First author: Dr. Andres Forero-Torres, Comprehensive Cancer Center, University of Alabama at Birmingham

About Brentuximab Vedotin

Brentuximab vedotin is an antibody-drug conjugate (ADC) comprising an anti-CD30 antibody attached by an enzyme cleavable linker to a potent, synthetic drug payload, monomethyl auristatin E (MMAE), using Seattle Genetics’ proprietary technology. The ADC is designed to be stable in the bloodstream, but to release MMAE upon internalization into CD30-expressing tumor cells, resulting in targeted cell-killing.

Seattle Genetics recently completed enrollment of its pivotal clinical trial of brentuximab vedotin for relapsed and refractory Hodgkin lymphoma. Data are expected in the second half of 2010. The company is also conducting a single-agent phase II study of brentuximab vedotin in relapsed and refractory systemic ALCL, as well as a phase II study evaluating the potential for retreatment with brentuximab vedotin in patients who have relapsed after discontinuing previous brentuximab vedotin therapy.

About Dacetuzumab

Dacetuzumab is a humanized monoclonal antibody that targets the CD40 antigen, which is expressed on most B lineage hematologic malignancies, as well as some solid tumors. Seattle Genetics is developing dacetuzumab under a worldwide collaboration agreement with Genentech, a wholly owned member of the Roche Group.

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, is in a pivotal trial under a special protocol assessment with the FDA. Brentuximab vedotin is empowered by Seattle Genetics’ proprietary ADC technology comprising highly potent synthetic drugs and stable linkers for attaching the drugs to monoclonal antibodies. In addition, Seattle Genetics has four other product candidates in ongoing clinical trials: lintuzumab (SGN-33), dacetuzumab (SGN-40), SGN-70 and SGN-75. Dacetuzumab is being developed under a worldwide collaboration with Genentech (a wholly-owned member of the Roche Group). Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech, Bayer, CuraGen, a subsidiary of Celldex Therapeutics, Progenics, Daiichi Sankyo, MedImmune, a subsidiary of AstraZeneca, and Millennium: The Takeda Oncology Company, as well as an ADC co-development agreement with Agensys, an affiliate of Astellas Pharma. 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 expectations of data from the brentuximab vedotin pivotal trial. 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, among others, that the company may experience adverse events, regulatory issues or other factors prior to the provision of such data. More information about the risks and uncertainties faced by Seattle Genetics is contained in the company’s 10-Q for the quarter ended September 30, 2009 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.