Talazoparib Plus Enzalutamide After Progression to Prior ARPi in Metastatic Prostate Cancer

This is a multicenter, open-label, randomized, phase II trial to evaluate the efficacy of the combination of talazoparib plus enzalutamide versus enzalutamide as first line treatment for metastatic castration resistant prostate cancer (mCRPC) in participants whose disease has progressed to abiraterone or other androgen receptor inhibitors (ARi) based treatment for metastatic hormone sensitive prostate cancer (mHSPC). Participants who meet the eligibility criteria will be randomized 2:1 to the experimental arm (enzalutamide and talazoparib) or control arm (enzalutamide) and will receive treatment until disease progression, unacceptable toxicity, death or discontinuation from the study treatment for any other reason. The experimental arm will be evaluated as 2 separate arms, post-AA and post-ARi, each with a single-stage phase II trial design. The control arm will not be directly compared to the experimental arm but will be used to explore biomarker differences in outcome measures between the experimental and control arm and confirm the statistical assumptions for the response rate under the null hypothesis. Prostate cancer is the second most common malignancy in men worldwide with an estimated annual global incidence of 1.3 million and over 375,000 deaths. Aggressive variant prostate cancer is a clinically defined subset of metastatic castration resistant prostate cancers (mCRPC) characterized by the absence of response to androgen receptor (AR) targeted agents and neuroendocrine features. The treatments that are currently available are not effective, representing an unmet clinical need. The combination of talazoparib, a potent selective PARP inhibitor (PARPi) and enzalutamide (androgen receptor signaling inhibitor; ARPi) demonstrated in the TALAPRO-2 study improved efficacy in metastatic castration resistant prostate cancer (mCRPC) participants with and without DNA damage response (DDR) gene alterations as first line treatment (1L) compared to enzalutamide alone. Estimated duration of the study: 48 months. Accrual is expected to be completed in 30 months. Median treatment duration has been estimated in 10 months. After completion of (or discontinuation from) treatment, participants will be followed up for survival until end of study (EoS) that will occur at 18 months after the enrollment of the last patient included in the trial, unless premature termination of the study. It is hypothesized that after progression to abiraterone, the addition of talazoparib to enzalutamide as 1L for mCRPC will result in improved PSA response rate and delayed progression compared to enzalutamide alone.