Press Release

Seattle Genetics Expands Antibody-Drug Conjugate Patent Portfolio

- Issued U.S. Patent Extends Patent Protection for Brentuximab Vedotin (SGN-35) to at Least 2025 -

BOTHELL, Wash., Mar 11, 2010 (BUSINESS WIRE) -- Seattle Genetics, Inc. (Nasdaq: SGEN) announced today that the U.S. Patent and Trademark Office has issued a patent related to its antibody-drug conjugate (ADC) technology. U.S. Patent No. 7,659,241 covers cleavable linkers and potent auristatin drug payloads used in certain of Seattle Genetics' ADC programs, most notably brentuximab vedotin (SGN-35), as well as many ADC programs in development by its collaborators. Brentuximab vedotin, an ADC that utilizes the vcMMAE drug-linker unit, is in a pivotal trial for relapsed and refractory Hodgkin lymphoma and a phase II trial for relapsed and refractory systemic anaplastic large cell lymphoma. The company anticipates submitting a New Drug Application for brentuximab vedotin in the first half of 2011.

"This patent is an important addition to the intellectual property portfolio surrounding our ADC technology, and significantly enhances the patent position for multiple internal and collaborator programs that use the vcMMAE drug-linker unit," said Eric Dobmeier, Chief Business Officer of Seattle Genetics. "Issuance of this patent, which extends protection in the United States to at least 2025, also reflects the culmination of significant and novel research conducted at Seattle Genetics to continue advancing our industry-leading ADC technology."

ADCs utilize the targeting ability of monoclonal antibodies to deliver potent, cell-killing payloads to specific cells. Seattle Genetics' proprietary technology employs synthetic, highly potent drugs attached to antibodies through stable linker systems. The linkers are designed to release the drug payload only under specific conditions once inside target cells, thereby sparing non-target cells many of the toxic effects of traditional chemotherapy.

Seattle Genetics is developing brentuximab vedotin in collaboration with Millennium: The Takeda Oncology Company, under which Seattle Genetics has U.S. and Canadian commercialization rights and Millennium has exclusive rights to commercialize the product in the rest of the world. Seattle Genetics and Millennium are jointly funding worldwide development costs for brentuximab vedotin on a 50:50 basis. Additionally, Seattle Genetics has nine ongoing ADC collaborations with leading biotechnology and pharmaceutical companies. To date, Seattle Genetics has generated approximately $110 million through ADC technology license agreements.

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 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.

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential of ADCs and the strength of Seattle Genetics' intellectual property portfolio. 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 to effectively advance or defend its intellectual property position. 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.

SOURCE: Seattle Genetics, Inc.

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