Phase Ib studies in non-Hodgkin lymphoma and multiple myeloma continue under worldwide collaboration with Genentech

BOTHELL, WA, USA | October 5, 2009 | Seattle Genetics, Inc. (Nasdaq:SGEN) announced today that it has discontinued the SeaGen MARINER clinical trial based on a determination that the trial would be unlikely to meet its primary endpoint of superior complete response rate in the dacetuzumab combination arm as compared to the placebo combination arm. The SeaGen MARINER trial was a randomized, double-blind phase IIb clinical trial of dacetuzumab or placebo in combination with Rituxan® (rituximab) plus ifosfamide, carboplatin and etoposide (R-ICE) chemotherapy for patients with relapsed or refractory diffuse large B-cell lymphoma (DLBCL). The trial was closed based upon a recommendation by the Independent Data Monitoring Committee (IDMC) following a pre-specified interim analysis conducted on Friday, October 2, 2009. As a result of the closure, dacetuzumab will no longer be provided to patients enrolled on the trial.

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. An oral presentation of a phase Ib clinical trial evaluating dacetuzumab in combination with Rituxan and Gemzar® (gemcitabine) will be made on December 7, 2009 at the American Society of Hematology annual meeting taking place in New Orleans, LA.

“We are disappointed that the interim analysis of the phase IIb clinical trial resulted in discontinuation of the study, especially given the unmet medical need for DLBCL patients,” said Clay B. Siegall, Ph.D., President and Chief Executive Officer of Seattle Genetics. “In collaboration with Genentech, we will conduct a detailed analysis of data from the SeaGen MARINER trial. In addition, we are continuing four ongoing phase Ib studies of dacetuzumab for non-Hodgkin lymphoma and multiple myeloma. We thank the patients and investigators for their participation and commitment to the clinical evaluation of dacetuzumab.”

The SeaGen MARINER trial was initiated in December 2007 and designed to accrue 224 relapsed or refractory DLBCL patients, of which approximately two-thirds were enrolled. Patients were treated with either R-ICE plus dacetuzumab or R-ICE plus placebo. The interim analysis was conducted on data from approximately half of the 224 total patients who were to be enrolled on the trial.

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 (SGN-35), is being evaluated 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 three other product candidates in clinical trials: lintuzumab (SGN-33), dacetuzumab (SGN-40) and SGN-70. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech, Bayer, CuraGen, Progenics, Daiichi Sankyo, MedImmune, a subsidiary of AstraZeneca, and Millennium: The Takeda Oncology Company, as well as an ADC co-development agreement with Agensys, a subsidiary of Astellas Pharma. More information can be found at www.seattlegenetics.com.

SOURCE: Seattle Genetics, Inc.