"The gene signature research being conducted under our collaboration with Genentech suggests that there may be a diagnostic test that can predict which patients are most likely to benefit from dacetuzumab therapy, aiding in the development of this antibody and providing another step towards the promise of personalized medicine for lymphoma patients," said Clay B. Siegall, Ph.D., President and Chief Executive Officer at Seattle Genetics. "This work, combined with our extensive preclinical findings on the enhanced activity of dacetuzumab in combination with other agents, continues to inform and support our clinical development activities. We anticipate that our ongoing clinical trials of dacetuzumab in combination with standard therapeutic regimens will begin to yield data later in 2009."

Dacetuzumab is a humanized anti-CD40 monoclonal antibody being developed by Seattle Genetics and Genentech, Inc., a wholly-owned member of the Roche Group, under a worldwide license agreement. The companies are conducting a broad development plan consisting of five ongoing phase Ib-IIb clinical trials evaluating dacetuzumab in combination with standard regimens for patients with non-Hodgkin lymphoma or multiple myeloma.

The data reported at AACR show a correlation between a diagnostic gene signature and sensitivity to treatment with dacetuzumab in patients with diffuse large B-cell lymphoma (DLBCL). The gene signature, which was originally identified in non-Hodgkin lymphoma cell lines, was retrospectively analyzed in patient samples from completed single-agent clinical trials of dacetuzumab. Data demonstrate that the gene signature correlated with sensitivity to treatment with dacetuzumab and had an overall accuracy of 80 percent. Furthermore, patients who were positive for the gene signature experienced longer progression-free survival compared to patients who were not. This diagnostic gene signature is being evaluated in ongoing clinical trials of dacetuzumab in combination with standard chemotherapy (Abstract # LB-138).

In a separate presentation, data showed the synergistic activity of dacetuzumab in combination with conventional cytotoxic drugs commonly used in the treatment of lymphoma. In addition, dacetuzumab was shown to sensitize non-Hodgkin lymphoma tumors to Gemzar^(R) (gemcitabine), and improve the efficacy of Rituxan^(R) (rituximab) plus Gemzar in preclinical models of non-Hodgkin lymphoma (Abstract # 3243). A phase Ib clinical trial of dacetuzumab in combination with Rituxan and Gemzar for patients with relapsed or refractory DLBCL is ongoing.

Downloadable copies of Seattle Genetics' AACR posters are available from the "Technology" section of the company's website at www.seattlegenetics.com.

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, SGN-35, is in a pivotal trial under a special protocol assessment with the FDA. SGN-35 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 ongoing clinical trials: dacetuzumab (SGN-40), lintuzumab (SGN-33) and SGN-70. Dacetuzumab is being developed under a worldwide collaboration with Genentech. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech (a wholly-owned member of the Roche Group), 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.

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the predictive potential of the diagnostic gene signature, the safety and antitumor activity of dacetuzumab combined with other therapies and the expectation of clinical data from the ongoing clinical trials of dacetuzumab. 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 risks related to adverse clinical results as our product candidates move into and advance in clinical trials, risks inherent in early stage development and failure by Seattle Genetics' collaborators to advance product candidates incorporating its technology. More information about the risks and uncertainties faced by Seattle Genetics is contained in the company's 10-K for the year ended December 31, 2008 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.

SOURCE: Seattle Genetics, Inc.

Seattle Genetics Corporate Communications
Peggy Pinkston, 425-527-4160
ppinkston@seagen.com