Press Release

Seattle Genetics and Millennium Report Positive Data on Retreatment with Brentuximab Vedotin (SGN-35) in Lymphoma
Objective Responses and Tolerability Demonstrated in Retreatment Setting

CHICAGO, Jun 05, 2010 (BUSINESS WIRE) --Seattle Genetics, Inc. (Nasdaq:SGEN) and Millennium: The Takeda Oncology Company, a wholly owned subsidiary of Takeda Pharmaceutical Company Limited (TSE:4502), today reported data on Hodgkin lymphoma and systemic anaplastic large cell lymphoma (ALCL) patients retreated with single-agent brentuximab vedotin (SGN-35). Preliminary data demonstrate that objective responses were achieved in seven out of 11 retreatment experiences and that brentuximab vedotin was well-tolerated in the retreatment setting. The data were presented at the 2010 Annual Meeting of the American Society of Clinical Oncology (ASCO) held in Chicago, Illinois.

"We are encouraged that more than half of the patients in this retreatment case series obtained objective responses with brentuximab vedotin," said Thomas C. Reynolds, M.D., Ph.D., Chief Medical Officer of Seattle Genetics. "Through our broad ongoing clinical development program, our goal is to continue to build on our understanding of brentuximab vedotin's potential to address the medical needs of Hodgkin lymphoma and ALCL patients who have limited therapeutic alternatives."

"We have seen the clinical strength of brentuximab vedotin in a variety of treatment settings, and these positive retreatment data provide additional evidence of its potential for patients who relapse," said Nancy Simonian, M.D., Chief Medical Officer, Millennium. "These preliminary data are supportive of the steps we are taking to bring brentuximab vedotin to those patients with Hodgkin lymphoma or ALCL who have limited treatment options."

Data from 11 retreatment experiences with brentuximab vedotin were presented, including nine from patients with Hodgkin lymphoma and two from patients with systemic ALCL. Patients were heavily pretreated with a range of two to 11 prior therapies. Five patients had received a prior autologous stem cell transplant. Patients had achieved stable disease with decreasing tumor volume or better during prior brentuximab vedotin treatment, discontinued treatment and subsequently experienced disease progression.

In these 11 retreatment experiences, objective responses were achieved in seven cases (64 percent), including two complete remissions and five partial remissions. Time to objective response ranged from five to 15 weeks. Three experiences resulted in stable disease and one in progressive disease. The duration of retreatment objective responses ranged from less than one week (retreatment ongoing) to 58+ weeks. Based on the small sample size, no difference in duration of retreatment response between patients with Hodgkin lymphoma and ALCL was observed. Retreatment is ongoing in three patients. Tumor reductions were observed in ten out of 11 retreatment cases. Brentuximab vedotin was well tolerated in the retreatment setting. All drug-related adverse events were Grade 1 or 2, with the most common being peripheral neuropathy, hair loss, joint pain and injection site irritation (Abstract #8062).

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 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 II trial for systemic ALCL to which enrollment was recently completed, 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 CD30-Positive Lymphoma

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. Hodgkin lymphoma is distinguished from other types of lymphoma by the presence of one characteristic type of cell, known as the Reed-Sternberg cell. A defining attribute of the Reed-Sternberg cell is its expression of the CD30 antigen. According to the American Cancer Society, approximately 8,500 cases of Hodgkin lymphoma will be diagnosed in the United States during 2009. ALCL is a T-cell non-Hodgkin lymphoma that expresses the CD30 antigen.

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.

For Seattle Genetics: Certain of the statements made in this press release are forward looking, such as those, among others, relating to the potential therapeutic benefit of brentuximab vedotin and plans for future clinical trials. 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 brentuximab vedotin advances in clinical trials, such as patients exhibiting progressive disease or severe adverse events; that data from the phase I clinical trials of brentuximab vedotin may not necessarily be indicative of subsequent clinical trial results, including the pivotal clinical trial results; and that the safety and/or efficacy results of these trials, including the brentuximab vedotin pivotal clinical trial for relapsed or refractory Hodgkin lymphoma, will not support an application for marketing approval in the United States or any other country. In addition, our regulatory plans may change as a result of consultation with the FDA or additional information from our clinical trials. More information about the risks and uncertainties faced by Seattle Genetics is contained in the company's 10-Q for the quarter ended March 31, 2010 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.

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SOURCE: Seattle Genetics, Inc.

Seattle Genetics, Inc.
Peggy Pinkston
425-527-4160
ppinkston@seagen.com
or
Millennium
Lauren Musto
617-551-7848
lauren.musto@mpi.com