Astellas and Pfizer Announce Amendment to Clinical Research Protocol for Phase 3 PROSPER Trial of enzalutamide in Patients with Non-metastatic Castration-Resistant Prostate Cancer

Astellas Pharma Inc. (TSE: 4503, President and
CEO: Yoshihiko Hatanaka, “Astellas”) and Pfizer Inc. (NYSE: PFE) has 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 castrationresistant
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
“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


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