TALAPRO-2: a placebo-controlled phase III study of talazoparib (TALA) plus enzalutamide (ENZA) for patients with first-line metastatic castration-resistant prostate cancer (mCRPC).

Abstract

TPS5598 Background: TALA blocks poly(ADP-ribose) polymerase (PARP) activity and traps PARP on single-strand DNA breaks, preventing DNA damage repair (DDR) and causing death of cells with DDR alterations (eg BRCA1/2).a TALA has been approved in multiple countries as monotherapy for germline BRCA1/2-mutated human epidermal growth factor receptor 2-negative advanced breast cancer. ENZA is an androgen receptor (AR) inhibitor and an established therapy for mCRPC. As PARP activity has been shown to support AR function, inhibition of PARP is expected to reduce AR signaling and increase sensitivity to AR-directed therapies. In addition, AR blockade downregulates homologous recombination repair gene transcription which induces ‘ BRCAness ’. Therefore, combining TALA with ENZA in mCRPC may be efficacious regardless of DDR alterations. TALAPRO-2 (NCT03395197) is a Phase III, 2-part study to evaluate efficacy, safety, pharmacokinetics, and patient-reported outcomes (PROs) of TALA combined with ENZA. Methods: Enrollment goal is 1037 patients (19 patients, part 1 dose-finding; 1,018 patients, part 2 placebo-controlled). Key eligibility criteria: age ≥18 years; asymptomatic/mildly symptomatic mCRPC; ECOG performance status ≤1; metastatic disease (no brain metastases); and no prior life-prolonging systemic therapy for nonmetastatic CRPC or mCRPC. Prior therapies (excluding novel AR inhibitors) in the castration-sensitive (CSPC) setting are allowed. ADT must continue throughout the study. The randomized double-blind portion (part 2) will evaluate safety, efficacy, and PROs of TALA (0.5 mg QD) + ENZA (160 mg QD) vs placebo + ENZA (160 mg QD). Patients are stratified by prior novel hormonal therapy or docetaxel for CSPC (yes or no) and DDR alteration status (deficient vs nondeficient/unknown). The primary endpoint is radiographic progression-free survival (rPFS), defined as time to progression in soft tissue per RECIST v.1.1 or in bone per PCWG3 criteria by independent review or death. The key secondary endpoint is overall survival. Efficacy will be assessed radiographically every 8 weeks up to Week 25 and every 8–12 weeks thereafter. rPFS will be compared between the two arms by a 1-sided stratified log-rank test. Patient recruitment is ongoing in multiple regions including US, Europe/Eastern Europe, Israel, South America, South Africa, and Asia-Pacific region. aDDR alterations are defined as known/likely pathogenic variants or homozygous deletions. Funding: Pfizer Inc. Clinical trial information: NCT03395197 .