ZEN003694 and Enzalutamide Versus Enzalutamide Monotherapy in Metastatic Castration-Resistant Prostate Cancer

This is an open-label, randomized, Phase 2b study of ZEN003694 in combination with enzalutamide vs. enzalutamide monotherapy in patients with mCRPC who have progressed on prior abiraterone by PCWG3 criteria. Disease must have progressed on only abiraterone by PCWG3 criteria prior to study entry. The patient population will be separated into two cohorts: Cohort A: Patients with poor response to prior abiraterone defined as: •Abiraterone started in hormone-sensitive prostate cancer (HSPC) disease setting: < 12 months duration on abiraterone or failure to achieve PSA nadir of 0.2 ng/mL while taking abiraterone, or; •Abiraterone started in castrate-resistant prostate cancer (CRPC) disease setting: < 6 months duration on abiraterone or failure to achieve PSA50 response while on abiraterone Cohort B: Patients with response to prior abiraterone, defined as: •Abiraterone started in hormone-sensitive prostate cancer (HSPC) disease setting: = 12 months duration on abiraterone and nadir PSA < 0.2 ng/mL, or; •Abiraterone started in castrate-resistant prostate cancer (CRPC) disease setting: = 6 months duration on abiraterone and confirmed PSA50 response