Seattle Genetics Reports SGN-40 Clinical Data at the American Society of Hematology Annual Meeting.

BOTHELL, Wash. -- Objective responses observed in ongoing phase I clinical trial of SGN-40 in non-Hodgkin's lymphoma 

Seattle Genetics, Inc. (Nasdaq: SGEN) reported data from its ongoing clinical trials of SGN-40 in multiple myeloma and non-Hodgkin's lymphoma at the American Society of Hematology (ASH) 2005 Annual Meeting being held in Atlanta December 10-13. Data from these phase I studies demonstrate that SGN-40 is well tolerated and has antitumor activity. In the non-Hodgkin's lymphoma study, objective responses were observed following one cycle of SGN-40 therapy. Dose escalation is continuing in both trials.

"We are excited by the data from our clinical trials of SGN-40, especially in our non-Hodgkin's lymphoma study where we have seen objective responses at well-tolerated doses," said Clay B. Siegall, Ph.D., President and Chief Executive Officer at Seattle Genetics. "We are proceeding rapidly with patient accrual and dose escalation in our ongoing clinical trials, with a goal of transitioning into phase II studies during 2006."

SGN-40 Phase I Clinical Trials

SGN-40 is a humanized monoclonal antibody that targets the CD40 antigen, which is expressed on most B-cell lineage hematologic malignancies, including multiple myeloma, non-Hodgkin's lymphoma and chronic lymphocytic leukemia. Seattle Genetics reported data from two open-label, multi-dose, single-arm phase I clinical trials of SGN-40 in patients with relapsed or refractory multiple myeloma or non-Hodgkin's lymphoma. The studies are designed to evaluate the safety, antitumor activity and pharmacokinetic profile of escalating doses of SGN-40. Patients receive multiple doses of SGN-40 over five weeks and are followed for at least eight weeks. Patients who experience a clinical benefit are eligible for a second cycle of therapy.

As previously reported, Seattle Genetics is treating patients in both trials under amended protocols that utilize an escalating dosing regimen for each patient during the first two weeks to attenuate potential cytokine release, which was observed in several patients treated under the original protocol. Thus far, SGN-40 has been well tolerated using this strategy and dose escalation is ongoing in both studies.

Non-Hodgkin's Lymphoma

Abstract #1504: A Phase I Study of Humanized Anti-CD40 Immunotherapy with SGN-40 in Non-Hodgkin's Lymphoma.

Seattle Genetics reported data from twelve non-Hodgkin's lymphoma patients, six treated at 2 mg/kg/week using the original schedule and six treated at doses up to 3 mg/kg/week on the amended dosing schedule. Patients in this study had a median age of 71 years and a median of 3.5 prior therapies. Two patients treated at 3 mg/kg/week demonstrated partial responses after 36 days on the study. Both patients continued on to a second cycle of therapy. One responding patient, who was restaged after the second cycle, continues to respond at day 79. The other responding patient has not yet been restaged. SGN-40 was well tolerated under the amended administration schedule at up to 3 mg/kg/week with mild adverse events consistent with antibody administration.

Multiple Myeloma

Abstract #2572: A Phase I Trial of Humanized Anti-CD40 Monoclonal Antibody (SGN-40) in Patients with Multiple Myeloma.

Seattle Genetics reported data from the first 23 multiple myeloma patients treated in the ongoing phase I study. Seven patients were treated under the amended dosing schedule, three of whom received doses up to 3 mg/kg/week and four of whom received doses up to 4 mg/kg/week. Patients in this study were heavily pretreated with a median of more than five prior therapies and median age of 61 years. SGN-40 is well tolerated at both dose levels using the intra-patient dose escalation schedule. Overall, two patients achieved stable disease at the conclusion of the first cycle and four patients had reductions in M-protein levels during therapy, although no patients have met criteria for objective response. One patient with stable disease advanced to a second cycle of therapy after clinical improvement.

About Seattle Genetics

Seattle Genetics is a biotechnology company focused on the development of monoclonal antibody-based therapies for the treatment of cancer and immunologic diseases. The company is conducting multiple clinical trials of its three lead product candidates, SGN-30, SGN-40 and SGN-33, and preclinical development of several late-stage programs. In addition, Seattle Genetics has developed proprietary antibody-drug conjugate (ADC) technology comprised of highly potent synthetic drugs and stable linkers for attaching the drugs to monoclonal antibodies. The company 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 about Seattle Genetics' pipeline and technologies can be found 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, continued progress and planned advancement of SGN-40 into phase II 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 SGN-40 advances in clinical trials, such as patients exhibiting progressive disease or severe adverse events. 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.