Preliminary Data Anticipated in Second Half of 2010

BOTHELL, WA, USA & CAMBRIDGE, MA, USA | May 24, 2010 | Seattle Genetics, Inc. (Nasdaq: SGEN) and Millennium: The Takeda Oncology Company, a wholly owned subsidiary of Takeda Pharmaceutical Company Limited (TSE:4502), today announced that they have completed enrollment of a phase II clinical trial of brentuximab vedotin (SGN-35) for relapsed or refractory systemic anaplastic large cell lymphoma (ALCL). Brentuximab vedotin is an antibody-drug conjugate (ADC) targeted to CD30, which is highly expressed on ALCL cells.

"This phase II trial enrolled in less than a year, driven by strong interest among clinical investigators and the ALCL patient community," said Thomas C. Reynolds, M.D., Ph.D., Chief Medical Officer of Seattle Genetics. "We anticipate preliminary data from this trial will be available in the second half of 2010, which will guide the next steps towards our goal of bringing this promising ADC to ALCL patients. We believe that systemic ALCL may offer an additional registration pathway for brentuximab vedotin."

"The quick rate of enrollment in this trial attests to the high unmet need for innovative new therapies for patients with ALCL," said Nancy Simonian, M.D., Chief Medical Officer of Millennium. "Brentuximab vedotin has the potential to provide an improvement in patient care, which is our primary goal, and is another step toward global oncology leadership for Millennium."

The phase II trial, which was initiated in June 2009, is a single-agent, single-arm study evaluating 55 patients with relapsed or refractory systemic ALCL. Patients receive 1.8 milligrams per kilogram of brentuximab vedotin every three weeks for up to approximately one year. The primary endpoint of the study is objective response rate determined by independent review. Secondary endpoints include duration of response, progression-free survival, overall survival and tolerability.

Of seven systemic ALCL patients treated with brentuximab vedotin in phase I clinical trials, six (86 percent) achieved a complete remission. Brentuximab vedotin was generally well-tolerated in these studies. The majority of adverse events were Grade 1 and 2, with the most common being fatigue, fever, peripheral neuropathy, diarrhea and nausea.

About Brentuximab Vedotin

Brentuximab vedotin is an 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 is developing brentuximab vedotin in collaboration with Millennium, under which Seattle Genetics has U.S. and Canadian development and commercialization rights and the Takeda Group has rights to develop and commercialize brentuximab vedotin in the rest of the world. Seattle Genetics and the Takeda Group are funding joint development costs for brentuximab vedotin on a 50:50 basis, except in Japan where the Takeda Group will be solely responsible for development costs.

Under the collaboration, Seattle Genetics and Millennium are conducting a pivotal trial of brentuximab vedotin for relapsed and refractory Hodgkin lymphoma under a Special Protocol Assessment (SPA) with the U.S. Food and Drug Administration (FDA). The pivotal trial was also discussed with the European Medicines Agency during the process of obtaining EU Centralized Scientific Advice on the brentuximab vedotin development program. Top-line data from the pivotal trial are expected in the second half of 2010. In addition, the companies are conducting a phase III clinical trial (the AETHERA trial) for patients at high risk of residual Hodgkin lymphoma following autologous stem cell transplant, a phase II retreatment trial for relapsed patients who previously responded to brentuximab vedotin, and a phase I combination trial for front-line treatment of Hodgkin lymphoma.

About ALCL

Lymphoma is a general term for a group of cancers that originate in the lymphatic system. There are two major categories of lymphoma: Hodgkin lymphoma and non-Hodgkin lymphoma. ALCL is a generally aggressive type of T-cell non-Hodgkin lymphoma that expresses CD30. Although front-line combination chemotherapy can result in durable responses, ALCL patients who relapse or are refractory to front-line treatment have few therapeutic options, representing a significant unmet medical need.

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 an SPA with the FDA. Brentuximab vedotin is being developed in collaboration with Millennium: The Takeda Oncology Company. In addition, Seattle Genetics has four other product candidates in ongoing clinical trials: lintuzumab (SGN-33), dacetuzumab (SGN-40), SGN-70 and SGN-75. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Bayer, Celldex Therapeutics, Daiichi Sankyo, Genentech, GlaxoSmithKline, MedImmune, a subsidiary of AstraZeneca, Millennium: The Takeda Oncology Company and Progenics, as well as an ADC co-development agreement with Agensys, an affiliate of Astellas. More information can be found at http://www.seattlegenetics.com.

About Millennium

Millennium: The Takeda Oncology Company, a leading biopharmaceutical company based in Cambridge, Mass., markets a first-in-class proteasome inhibitor, and has a robust clinical development pipeline of product candidates. Millennium Pharmaceuticals, Inc. was acquired by Takeda Pharmaceutical Company Ltd. in May, 2008. The Company’s research, development and commercialization activities are focused in oncology. Additional information about Millennium is available through its website, http://www.millennium.com.

SOURCE: Seattle Genetics, Inc.