Astellas and Pfizer have amended the protocol for their registrational PROSPER study evaluating Xtandi® (enzalutamide) in patients with nonmetastatic castration-resistant prostate cancer (CRPC), which could bring topline data from the study forward by two years. The protocol amendment doesn’t change the primary endpoint of metastasis-free survival (MFS), but revises the plan for analyzing primary and secondary endpoints, such that the target sample size has now been reduced to 1440 patients from 1560 patients. The amendment means topline data from PROSPER is anticipated this year, rather than in June 2019. 

“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, M.D., 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.”

The androgen receptor blocker Xtandi was first approved by FDA in 2012 as second-line therapy for patients with metastatic CRPC who had previously been treated using docetaxel. In 2014, the drug was approved in the U.S. as first-line therapy, and in October 2016, the FDA approved a supplemental new drug application that updates the U.S. product label to include new clinical data from the TERRAIN study, which showed improved radiographic progression-free survival in metastatic CRPC patients treated with enzalutamide, compared iwht those treated using bicialutamide.

Astellas and Medivation—which Pfizer bought for $14 billion in August 2016—set up their partnership to jointly develop and commercialize enzalutamide in 2009. Astellas and Pfizer jointly commercialize the drug in the U.S. Astellas is responsible for manufacturing and for all other regulatory filings worldwide, as well as commercialization of enzalutamide outside the U.S. Astellas reported global Xtandi sales of Yen 252.1 billion (approximately $2.3 billion) in fiscal year ended March 31, 2017.

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