-Solid Tumor Antibody-Drug Conjugate (ADC) Enfortumab Vedotin to be Evaluated as a Monotherapy in Patients Previously Treated with a Checkpoint Inhibitor-

BOTHELL, WA, USA & TOKYO, Japan I October 10, 2017 I Seattle Genetics, Inc. (NASDAQ: SGEN) and Astellas Pharma Inc. (TSE: 4503, President and CEO: Yoshihiko Hatanaka, “Astellas”) today announced dosing of the first patient in EV-201, a registrational phase 2 clinical trial of enfortumab vedotin for patients with locally advanced or metastatic urothelial cancer who have been previously treated with checkpoint inhibitor (CPI) therapy. The EV-201 study will assess the antitumor activity and safety of enfortumab vedotin to support potential registration under the U.S. Food and Drug Administration’s (FDA) accelerated approval regulations.

“Locally advanced or metastatic urothelial cancers are often aggressive and treatment-resistant. Treatment options are limited for those many patients who do not respond to chemotherapy and checkpoint inhibitors, or CPIs. In addition, there are no FDA-approved therapies for patients who progress following CPI treatment,” said Jonathan Drachman, M.D., Chief Medical Officer and Executive Vice President, Research and Development at Seattle Genetics. “Initiation of this pivotal phase 2 trial of enfortumab vedotin is a significant advance toward our goal of providing a new treatment option for locally advanced or metastatic urothelial cancer.”

The primary endpoint of the single-arm, open-label trial is confirmed objective response rate (ORR), per independent review. Secondary endpoints include assessments of overall survival, progression free-survival, safety and tolerability. The study will enroll approximately 120 patients at multiple centers globally, and enfortumab vedotin will be administered three of every four weeks for the duration of treatment.

“The initiation of the EV-201 clinical trial demonstrates our continued commitment to patients living with locally advanced or metastatic urothelial cancer,” said Steven Benner, M.D., Senior Vice President and Global Therapeutic Area Head, Oncology Development at Astellas. “Our decision to move forward with this registrational trial is based on the results of our ongoing Phase 1 study, and we look forward to future clinical development milestones for enfortumab vedotin.”

The companies also plan to initiate a combination trial of enfortumab vedotin with CPI therapy in late 2017.

For more information about the phase 2 pivotal trial, including enrolling centers, please visit www.clinicaltrials.gov.

About Urothelial Cancer

Urothelial cancer is most commonly found in the bladder (90 percent). According to the American Cancer Society, approximately 79,000 people in the U.S. will be diagnosed with bladder cancer during 2017 and almost 17,000 will die from the disease. Outcomes are poor for patients diagnosed with metastatic disease, with a five-year survival rate of five percent.

About Enfortumab Vedotin

Enfortumab vedotin is an investigational ADC composed of an anti-Nectin-4 monoclonal antibody attached to a microtubule-disrupting agent, MMAE, using Seattle Genetics’ proprietary, industry-leading linker technology. Enfortumab vedotin targets Nectin-4, a cell adhesion molecule identified as an ADC target by Agensys (an affiliate of Astellas), which is expressed on many solid tumors.

Nectin-4 is highly expressed in urothelial cancers, particularly in bladder cancer. Preclinical data demonstrate that enfortumab vedotin binds to Nectin-4 on cancer cells and releases the cell-killing agent into these target cells upon internalization.

About Seattle Genetics

Seattle Genetics is an innovative biotechnology company dedicated to improving the lives of people with cancer through novel antibody-based therapies. The company’s industry-leading antibody-drug conjugate (ADC) technology harnesses the targeting ability of antibodies to deliver cell-killing agents directly to cancer cells. Seattle Genetics commercializes ADCETRIS® (brentuximab vedotin) for the treatment of several types of CD30-expressing lymphomas. The company is also advancing a robust pipeline of novel therapies for solid tumors and blood-related cancers designed to address significant unmet medical needs and improve treatment outcomes for patients. More information can be found at www.seattlegenetics.com and follow @SeattleGenetics on Twitter.

About Astellas

Astellas Pharma Inc., based in Tokyo, Japan, is a company dedicated to improving the health of people around the world through the provision of innovative and reliable pharmaceutical products. We focus on Urology, Oncology, Immunology, Nephrology and Neuroscience as prioritized therapeutic areas while advancing new therapeutic areas and discovery research leveraging new technologies/modalities. We are also creating new value by combining internal capabilities and external expertise in the medical/healthcare business. Astellas is on the forefront of healthcare change to turn innovative science into value for patients. For more information on Astellas, please visit our website at www.astellas.com/en.

About the Astellas and Seattle Genetics Collaboration

Astellas and Seattle Genetics entered into the ADC collaboration in January 2007 and expanded it in November 2009. Under the collaboration, the companies are co-developing and have options to globally co-commercialize enfortumab vedotin.

SOURCE: Seattle Genetics