Clinical Data on Seattle Genetics Monoclonal Antibody SGN-30 To Be Presented at American Society of Hematology Annual Meeting

Clinical Data on Seattle Genetics Monoclonal Antibody SGN-30 To Be Presented at American Society of Hematology Annual Meeting

Business Editors/Health/Medical Writers

44th Annual Meeting and Exposition of the American Society of

Hematology

BOTHELL, Wash.–(BUSINESS WIRE)–Dec. 5, 2002

Seattle Genetics, Inc. (Nasdaq:SGEN) announced today that clinical data on its product candidate SGN-30 will be presented during the 44th Annual Meeting and Exposition of the American Society of Hematology (ASH) held in Philadelphia, PA.

SGN-30 is a monoclonal antibody being developed for the treatment of various hematologic malignancies, including Hodgkin’s disease and certain other lymphomas. Nancy L. Bartlett, M.D., from the Department of Internal Medicine at Washington University in St. Louis, Missouri and principal investigator of the trial, will present results from the first phase I study in a poster presentation on Saturday, December 7, 2002.

“We were pleased by the encouraging data from our phase I single-dose study and, based on the results, have already initiated the next clinical trial of SGN-30,” stated Amy P. Sing, M.D., Senior Director of Medical and Regulatory Affairs of Seattle Genetics. “The first phase I study demonstrated that SGN-30 is safe to administer and evidence of antitumor activity was observed. A phase I/II study designed to evaluate the safety and activity of multiple doses of SGN-30 in up to 70 patients with CD30 expressing hematologic malignancies is now underway.”

Summary of Findings

SGN-30 is a monoclonal antibody that targets CD30, a cell surface receptor that is expressed in high density on a variety of hematologic malignancies, such as Hodgkin’s disease and anaplastic large cell lymphoma. Preclinical studies demonstrated that SGN-30 has antitumor activity in model systems at low doses. Single and repeat dose toxicology studies demonstrated that the antibody was well tolerated in non-human primates with no toxicity observed after repeated high doses. Based on the tumor specificity of SGN-30, the preclinical antitumor activity and its lack of toxicity, a phase I study was conducted in patients with CD30 expressing hematologic malignancies.

The study was designed as a rapid dose escalation to evaluate safety, pharmacokinetics, immunogenicity and antitumor activity of a single-dose of SGN-30, and to identify a proposed starting dose for a multi-dose study. Thirteen patients with relapsed CD30 expressing hematologic malignancies were treated in the open label study across seven doses ranging from one to 15 milligrams per kilogram. No significant drug related toxicities were noted in any of the patients. Objective antitumor responses to the treatment were observed in two patients. The trial was conducted at the Siteman Cancer Center at Washington University in St. Louis, Missouri, MD Anderson Cancer Center in Houston, Texas, and Norris Cancer Center at the University of Southern California in Los Angeles, California.

A phase I/II multi-dose study is now open to accrual. The study is designed to evaluate the safety, pharmacokinetic profile and antitumor activity of a six-dose regimen of SGN-30 in patients with Hodgkin’s disease, anaplastic large cell lymphoma or certain other lymphomas.

About Seattle Genetics

Seattle Genetics discovers and develops monoclonal antibody-based therapeutics to treat cancer and related diseases. The Company has three platform technologies: engineered monoclonal antibodies, antibody-drug conjugates (ADCs) and antibody-directed enzyme prodrug therapy (ADEPT). Seattle Genetics has built a diverse portfolio of product candidates targeted to many types of human cancers, including two currently being tested in multiple ongoing clinical trials. Seattle Genetics has agreements with many organizations including Bristol-Myers Squibb, Genencor International and Medarex. The company also has license agreements for its ADC technology with Genentech, Celltech Group and Eos Biotechnology. More information about Seattle Genetics can be found at www.seattlegenetics.com.

Certain of the statements made in this press release are forward-looking, such as those, among others, related to preclinical and clinical results. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Specifically, statements regarding ongoing and planned clinical trials are forward-looking and actual results may differ materially from these statements for various reasons. 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 secure collaborators or failure of those collaborators to perform their contractual obligations. 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.

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