Seattle Genetics Receives Key Anti-CD30 Patent Claims.

BOTHELL, Wash. -- Seattle Genetics, Inc. (Nasdaq:SGEN) announced today it has received a notice of allowance from the U.S. Patent and Trademark Office (USPTO) for a patent entitled "Recombinant Anti-CD30 Antibodies and Uses Thereof." The issued claims cover methods of using certain anti-CD30 antibodies for the treatment of Hodgkin's disease, both as a single agent and in combination with other therapies. The company currently has two anti-CD30 product candidates in its development pipeline: SGN-30, a genetically engineered antibody, is in phase II clinical development for Hodgkin's disease and T-cell lymphomas, and SGN-35, an antibody-drug conjugate (ADC), is planned to enter clinical trials during 2006.

"This patent is a significant addition to our intellectual property portfolio and provides an important competitive advantage for our anti-CD30 programs," stated Eric L. Dobmeier, Senior Vice President, Corporate Development and General Counsel of Seattle Genetics. "We are advancing SGN-30 in multiple oncology settings, including ongoing single-agent studies in systemic and cutaneous ALCL and planned combination studies in collaboration with the National Cancer Institute for both Hodgkin's disease and T-cell lymphomas. We are also on track to file an IND for SGN-35 in mid-2006 for the treatment of CD30-positive hematologic malignancies."

The CD30 antigen is expressed on Hodgkin's disease and several T-cell lineage hematologic malignancies, including systemic anaplastic large cell lymphoma (ALCL) and cutaneous ALCL. CD30 is an attractive target for cancer therapy because it is expressed on malignant cells, but has minimal expression on normal tissues.

SGN-30 is a genetically engineered antibody that has shown objective antitumor activity, including complete and partial responses, in ongoing phase II clinical trials of systemic ALCL and cutaneous ALCL. The company plans to report interim phase II data from the cutaneous ALCL trial at the Society for Investigative Dermatology annual meeting in May 2006 and final phase II data from the systemic ALCL trial at the American Society of Hematology annual meeting in December 2006. In preclinical studies, SGN-30 has also demonstrated synergistic activity when combined with chemotherapy in models of Hodgkin's disease. NCI-sponsored studies of SGN-30 in combination with chemotherapy are planned for 2006 in both relapsed Hodgkin's disease and front-line systemic ALCL. In addition, SGN-30 may have potential applications in immunologic disease due to the expression of CD30 on activated, but not resting, T-cells.

SGN-35 is an ADC comprised of an anti-CD30 antibody stably linked to a potent synthetic drug payload, monomethyl auristatin E (MMAE), using Seattle Genetics' proprietary ADC technology. SGN-35 has demonstrated selective activity including complete regressions at well tolerated doses in preclinical models. The company is completing IND-enabling toxicology studies of SGN-35 and plans to submit an investigational new drug (IND) application for the treatment of CD30-expressing hematologic malignances in mid-2006.

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 potential of SGN-30, the filing of an IND for SGN-35 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, the risk that the NCI delays or cancels its planned studies of SGN-30 in combination with chemotherapy and the risk that we are not able to complete our IND enabling studies for SGN-35. 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.