TALAPRO-2: Part 2 (P2) of the placebo-controlled phase 3 study of talazoparib (TALA) with enzalutamide (ENZA) in metastatic castration-resistant prostate cancer (mCRPC).

TPS5092 Background: ENZA is approved to treat men with CRPC. TALA is a poly(ADP-ribose) polymerase (PARP) inhibitor that inhibits PARP1/PARP2 and traps PARP on DNA, preventing DNA damage repair (DDR), and causing cell death in BRCA1/2-mutated cells. TALA is approved in the US to treat germline BRCA1/2-mutated HER2- locally advanced/metastatic breast cancer. A combination of TALA with ENZA in mCRPC may improve clinical outcomes. TALAPRO-2 (NCT03395197) is a 2-part study to evaluate the efficacy, safety, pharmacokinetics and (patient) pt-reported outcomes of the combination treatment. The focus here is on P2 of TALAPRO-2. Methods: Approximately 860 pts are planned to be enrolled in P2 from multinational sites. Pts are aged ≥18 years, have asymptomatic/mildly symptomatic mCRPC, Eastern Cooperative Oncology Group performance status ≤1, no brain metastases, and have not received taxanes/novel hormonal therapy (NHT). P2 is a randomized double-blind study that will evaluate safety, efficacy, and pt-reported outcomes of TALA (0.5 mg QD) + ENZA (160 mg QD) vs placebo + ENZA (160 mg QD). Pts will be randomized to 1 of 2 treatment groups: TALA + ENZA, or matching placebo + ENZA. Randomization will be stratified by prior treatment with NHT for castration-sensitive prostate cancer (CSPC) or prior treatment with taxane-based chemotherapy for CSPC (yes/no) and DDR mutation status (deficient vs. nondeficient/unknown). The primary endpoint is radiographic progression-free survival (rPFS), defined as time to progression in soft tissue per RECIST v1.1 or in bone per PCWG3 criteria or death. The key secondary endpoint is overall survival (OS). Efficacy will be assessed by radiography every 8 weeks up to week 25 and every 8-12 weeks thereafter. The analyses of rPFS will be compared between TALA in combination with ENZA and placebo in combination with ENZA by using a 1-sided stratified log-rank test. OS will be evaluated separately in the all comers and the DDR-deficient populations. Pt recruitment is ongoing. Results: n/a. Conclusions: n/a. Clinical trial information: NCT03395197.