Seattle Genetics Announces Initiation of a Phase Ib Trial of SGN-75 in Combination with Everolimus for Patients with Renal Cell Carcinoma

Seattle Genetics Announces Initiation of a Phase Ib Trial of SGN-75 in Combination with Everolimus for Patients with Renal Cell Carcinoma

Seattle GeneticsInvestors:Peggy Pinkston, 425-527-4160orMedia:Tricia Larson, 425-527-4180

(Nasdaq:SGEN) today announced the initiation of a phase Ib clinical trial evaluating SGN-75 in combination with everolimus (Afinitor) for patients with advanced metastatic renal cell carcinoma (RCC). The trial is designed to assess the safety and antitumor activity of SGN-75 in combination with everolimus. Seattle Genetics is a leader in the field of antibody-drug conjugates (ADCs) and SGN-75 is an ADC targeted to CD70.

“ADCs have the potential to change the way many types of cancer are treated, and we are excited to evaluate our ADC product candidate, SGN-75, in this phase Ib trial for patients with CD70-expressing RCC,” said Jonathan Drachman , M.D., Senior Vice President, Research and Translational Medicine at Seattle Genetics. “We are encouraged by the preliminary single-agent activity and tolerability demonstrated by SGN-75 in RCC patients and by our preclinical data suggesting synergy between auristatin-containing ADCs and mTOR inhibitors, including everolimus. We look forward to investigating whether this combination can provide therapeutic benefit to patients who currently have limited treatment options.”

The study is a phase Ib, open-label, dose-escalation clinical trial to evaluate the safety and antitumor activity of SGN-75 in combination with everolimus, an mTOR inhibitor, in patients with CD70-positive metastatic RCC. Everolimus is an oral prescription medication used to treat advanced RCC when certain other medicines, such as sunitinib or sorafenib,have not workedThe trial is enrolling patients who have previously been treated with one or two tyrosine kinase inhibitors (TKIs). The primary endpoint of the trial is safety, with key secondary endpoints of best clinical response, progression-free survival (PFS) and overall survival (OS). The study is expected to enroll up to 40 patients at multiple centers in the United States.

“Despite the use of immunotherapy, tyrosine kinase inhibitors and mTOR inhibitors, many patients with kidney cancer ultimately experience progression of their disease,” said Elisabeth Heath, M.D., Associate Professor of Oncology at Barbara Ann Karmanos Cancer Institute and investigator for this phase Ib clinical trial. “Kidney cancer tends to resist treatments after it stops responding to initial therapy, clearly demonstrating a need to identify new treatment approaches, such as targeted therapies directed to novel targets and combination therapy.”

For more information about the trial, including enrolling centers, please visit .

SGN-75 is an ADC composed of an anti-CD70 antibody attached to a synthetic cytoxic cell-killing agent, monomethyl auristatin F (MMAF), using Seattle Genetics’ proprietary technology. The ADC is designed to be stable in the bloodstream, and to release its cytoxic agent upon internalization into CD70-expressing tumor cells. This approach is intended to spare non-targeted cells and thus reduce many of the toxic effects of traditional chemotherapy while enhancing the antitumor activity.

Renal cell carcinoma (RCC) forms in the kidney, which filters and cleans the blood. Metastatic RCC occurs when the cancer has spread to other parts of the body. RCC is the most common type of kidney cancer in adults, representing approximately 90 percent of cases. The American Cancer Society estimates that nearly 65,000 new cases of kidney cancer will be diagnosed in the United States during 2012, and approximately 13,600 people will die from the disease.

Seattle Genetics is a biotechnology company focused on the development and commercialization of monoclonal antibody-based therapies for the treatment of cancer. The U.S. Food and Drug Administration granted accelerated approval of ADCETRIS in August 2011 for two indications. ADCETRIS is being developed in collaboration with Millennium: The Takeda Oncology Company. In addition, Seattle Genetics has three other clinical-stage ADC programs: SGN-75, ASG-5ME and ASG-22ME. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Abbott, Agensys (an affiliate of Astellas), Bayer, Celldex Therapeutics, Daiichi Sankyo, Genentech, GlaxoSmithKline, Millennium, Pfizer and Progenics, as well as ADC co-development agreements with Agensys and Genmab. More information can be found at .

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential of SGN-75. 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 the inability to show sufficient activity in this recently initiated clinical trial and the risk of adverse events as SGN-75 advances in clinical trials. More information about the risks and uncertainties faced by Seattle Genetics is contained in the company’s 10-Q for the quarter ended June 30, 2012 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.