-Updated Data from Phase 1 EV-101 Study Highlighted in ASCO 2018 Oral Presentation Support Rapid Development Program and Ongoing Pivotal Study- 

TOKYO and BOTHELL, Wash. – June 3, 2018 – Astellas Pharma Inc. (TSE: 4503, President and CEO: Kenji Yasukawa, Ph.D., “Astellas”) and Seattle Genetics, Inc. (Nasdaq: SGEN) today announced the presentation of updated phase 1 data of enfortumab vedotin, an investigational antibody-drug conjugate (ADC), at the American Society of Clinical Oncology (ASCO) 2018 Annual Meeting in Chicago. In this phase 1 study (EV-101), enfortumab vedotin was evaluated as monotherapy for patients with metastatic urothelial cancer including patients who previously received a checkpoint inhibitor.i This phase 1 study is part of a broader program focused on investigating enfortumab vedotin in both monotherapy and in combination with a checkpoint inhibitor for locally advanced or metastatic urothelial cancer.

“Many patients with locally advanced or metastatic urothelial cancer previously treated with checkpoint inhibitors have a poor prognosis and limited subsequent treatment options,” said Jonathan E. Rosenberg, M.D., medical oncologist at Memorial Sloan Kettering Cancer Center and presenter of the updated phase 1 data at ASCO. “Data from the ongoing study support the potential of enfortumab vedotin in locally advanced or metastatic urothelial cancer, based on the objective response rate and preliminary estimates of survival.”

“We are encouraged by these updated data for enfortumab vedotin, which further support the rapid expansion of a comprehensive clinical trial program and the registrational study that is already underway in metastatic urothelial cancer,” said Steven Benner, M.D., Senior Vice President and Global Therapeutic Area Head, Oncology Development, Astellas. “We look forward to working closely with our partner, Seattle Genetics, as we continue to evaluate enfortumab vedotin for patients with metastatic urothelial cancer.” 

Robert Lechleider, M.D., Senior Vice President, Clinical Development at Seattle Genetics added, “These ASCO data from the phase 1 study of enfortumab vedotin further support its Breakthrough Therapy Designation from the FDA, and the rationale for our ongoing pivotal trial, EV-201. We look forward to completing enrollment of the EV-201 pivotal trial for patients with metastatic urothelial cancer who have received both a platinum-based therapy and a checkpoint inhibitor. Positive data in this patient subgroup may represent a potential expedited registration pathway.”

The following updated results were presented by Dr. Rosenberg:

Updated Results from the Enfortumab Vedotin Phase 1 (EV-101) Study in Patients with Metastatic Urothelial Cancer: (Abstract #4504, oral abstract session on Sunday, June 3 from 9:12-9:24 a.m. CT)1

Study Design

  • A total of 112 patients with metastatic urothelial cancer treated with 1 or more prior chemotherapy or who were ineligible for cisplatin received a 30-minute infusion of enfortumab vedotin at 1.25 mg/kg on day 1, 8 and 15 of each 28-day cycle.ii 
  • Sixty-three percent of patients had received 2 or more prior therapies in the metastatic setting.1
  • The primary objective of the study was tolerability. A secondary objective was antitumor activity, which was assessed by investigators every 8 weeks.2

Study Results

  • Of 112 evaluable patients, confirmed complete responses were observed in 4 patients and confirmed partial responses were observed in 41 patients, with an overall response rate of 41 percent.1
  • The most commonly reported treatment-related adverse event was All Grade fatigue (54 percent). Anemia (8 percent), hyponatremia (7 percent), urinary tract infection (7 percent) and hyperglycemia (6 percent) were the most common ≥ Grade 3 AEs.1 Four patients experienced a fatal treatment-related adverse event (respiratory failure, urinary tract obstruction, diabetic ketoacidosis, multi-organ failure).2
  • Additionally, the ORR in the 89 patients with prior checkpoint inhibitor therapy was 40 percent, 44 percent in the 23 patients who had not been treated with a checkpoint inhibitor, and 39 percent in the 33 patients with liver metastases.1
  • For all enrolled patients, the interim median overall survival was 13.6 months, the overall median duration of response was 5.75 months and the median progression-free survival was 5.4 months.1

EV-201 Study: A Single-Arm, Open-Label, Multicenter Study of Enfortumab Vedotin for Treatment of Patients with Locally Advanced or Metastatic Urothelial Cancer Who Previously Received Immune Checkpoint Inhibitor Therapy (Abstract #TPS4590, poster session on Saturday, June 2 from 8:00-11:30 a.m. CT)iii

In addition, the EV-201 trial in progress poster was presented at the meeting. EV-201 is an ongoing single-arm, single-agent pivotal phase 2 clinical trial of enfortumab vedotin for patients with locally advanced or metastatic urothelial cancer who have been previously treated with checkpoint inhibitor therapy, including those who had also been treated with a platinum chemotherapy and those who were platinum naive.3

More information about the enfortumab vedotin clinical trials can be found at https://www.clinicaltrials.gov