Seattle Genetics Announces Advancements in Development Programs at American Society of Hematology Meeting.

Eleven Presentations Highlight Breadth of Therapeutic Antibody Programs

SEATTLE -- Seattle Genetics, Inc. (Nasdaq:SGEN) today announced clinical and preclinical data from the company's five lead antibody-based product candidates reported in multiple presentations during the American Society of Hematology (ASH) 48th Annual Meeting and Exposition in Orlando, Florida.

"The data presented at ASH highlight the continued advancement and potential of our antibody-based therapeutics and the breadth of our product pipeline," commented Clay B. Siegall, Ph.D., President and Chief Executive Officer at Seattle Genetics. "In addition to SGN-40, our lead product candidate, we are making strong progress with other promising clinical programs in our pipeline, including SGN-33, SGN-35 and SGN-30, all of which address unmet medical needs in cancer."

SGN-40 Program

As announced yesterday, data reported from phase I trials of SGN-40 demonstrate that it is well-tolerated and exhibits durable objective responses in patients with relapsed/refractory non-Hodgkin's lymphoma (abstract 695). In multiple myeloma patients, SGN-40 is well-tolerated and evidence of antitumor activity and B-cell depletion have been observed (abstract 3576). The company also reported preclinical data in non-Hodgkin's lymphoma and multiple myeloma showing that SGN-40 has additive activity when combined with conventional therapies (abstracts 2499 and 3506).

SGN-33 Program

SGN-33 (lintuzumab) is a humanized monoclonal antibody that targets the CD33 antigen. CD33 is highly expressed on several types of hematologic malignancies, including acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). In a phase I dose-escalation clinical trial (abstract 4568), SGN-33 was shown to be well-tolerated and antitumor activity was observed, demonstrated by improved blood counts, decreased transfusion requirements and/or decreased blasts in patients with AML or MDS. In addition, in a preclinical study (abstract 1995), SGN-33 was shown to bind to CD33 and block cytokine production by monocytes and macrophages.

Anti-CD30 Programs: SGN-30 and SGN-35

Seattle Genetics presented data from two phase II clinical studies of SGN-30, a monoclonal antibody directed against the CD30 antigen, which is highly expressed on a variety of hematologic malignancies including Hodgkin's disease and some T-cell non-Hodgkin's lymphomas. In these studies (abstracts 2718 and 2733), SGN-30 was well-tolerated and demonstrated multiple objective responses in patients with relapsed/refractory systemic anaplastic large cell lymphoma (ALCL) as well as a high objective response rate in patients with cutaneous CD30-positive lymphoproliferative disorders. The company is collaborating with the National Cancer Institute to conduct combination studies of SGN-30 and chemotherapy for the treatment of relapsed Hodgkin's disease, front-line ALCL and pediatric ALCL.

SGN-35 is an antibody-drug conjugate (ADC) that links SGN-30 to a potent, synthetic drug payload, monomethyl auristatin E (MMAE). In an oral presentation, preclinical data show that SGN-35 effectively targets CD30 and delivers MMAE to tumor cells resulting in potent cell-killing. In addition, in vitro studies demonstrate bystander effect, which may intensify antitumor activity of the ADC. Seattle Genetics recently initiated a phase I clinical trial of SGN-35 in patients with Hodgkin's disease and other CD30-positive hematologic malignancies.

SGN-70 Program

Seattle Genetics and its collaborators presented preclinical data on SGN-70, a humanized monoclonal antibody that targets the CD70 antigen, which is expressed in many types of hematologic malignancies. CD70 is also present on activated T cells, providing a therapeutic opportunity in autoimmune and inflammatory disorders. Preclinical studies show that SGN-70 selectively targets CD70 and induces effector cell-mediated antitumor activity, extending survival in animal models of multiple myeloma, Hodgkin's disease and non-Hodgkin's lymphoma (abstract 2492). Treatment with SGN-70 was also shown to block tumor growth in a model of Waldenstr[?]m's macroglobulinemia (abstract 2490), a B-cell disorder. Lastly, in an in vitro study of autoimmune and inflammatory disease (abstract 1728), SGN-70 selectively depleted CD70-positive activated T cells and limited expansion of antigen-specific T lymphocytes.

Downloadable copies of the ASH posters describing these data are available from the News and Investor Information section of Seattle Genetics' website.

About Seattle Genetics

Seattle Genetics is a biotechnology company developing monoclonal antibody-based therapies for the treatment of multiple types of cancer, including non-Hodgkin's lymphoma, multiple myeloma, acute myeloid leukemia and Hodgkin's disease. The company has also developed proprietary antibody-drug conjugate (ADC) technology comprised of highly potent synthetic drugs and stable linkers for attaching the drugs to monoclonal antibodies. Seattle Genetics currently has license agreements for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech, Bayer, CuraGen and MedImmune. More information is available at www.seattlegenetics.com.

Certain of the statements made in this press release are forward-looking, such as those, among others, relating to the therapeutic benefit and future advancement of SGN-40, SGN-33, SGN-30, SGN-35 and SGN-70. 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 SGN-40, SGN-33, SGN-30 and SGN-35 advance in clinical trials, such as patients exhibiting progressive disease or severe adverse events, and adverse results of further preclinical studies conducted with SGN-70. More information about the risks and uncertainties faced by Seattle Genetics is contained in the Company's filings 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.