Astellas and Pfizer Announce Amendment to Clinical Research Protocol for Phase 3 PROSPER Trial of enzalutamide

Astellas Pharma Inc. and Pfizer Inc. announced the amendment of the protocol for the registrational PROSPER trial, a multi-national, randomized, double-blind, placebo-controlled study evaluating the efficacy and safety of XTANDI (enzalutamide) in patients with non-metastatic (M0) Castration-Resistant Prostate Cancer (CRPC). The primary endpoint remains the same: metastasis-free survival (MFS). The main purpose of the amendment is to revise the plan for the analyses of the primary and several secondary endpoints, which allows for a reduction in the target sample size to approximately 1,440, from 1,560 patients. The companies now anticipate PROSPER top-line results will be disclosed later this year. Previously the expected primary completion date for PROSPER was June 2019.

“XTANDI is already a standard of care for men worldwide fighting metastatic castration-resistant prostate cancer, but we are continually looking to evaluate this medicine for men facing earlier stage disease,” said Steven Benner, M.D., senior vice president and global therapeutic area head, oncology development, Astellas. “By amending the protocol for PROSPER, we hope to be able to accelerate the evaluation of the data in this area of medical need.”

“PROSPER is one of a number of large, randomized trials in our robust, registration-focused development program, where we are evaluating enzalutamide in different prostate cancer populations, including men with earlier stages of the disease,” said Mace Rothenberg, MD, chief development officer, Oncology, Pfizer Global Product Development. “We look forward to building upon the extensive body of clinical evidence that has been generated over the past five years and established XTANDI as a standard of care for men with metastatic CRPC.”

XTANDI is approved by the U.S. Food and Drug Administration for the treatment of patients with metastatic CRPC, based on clinical studies showing statistically significant overall survival benefit versus placebo.

Details regarding the protocol amendment for PROSPER (NCT02003924) will be available on ClinicalTrials.gov.