Niraparib With Abiraterone Acetate Plus Prednisone as First-Line Therapy in Patients With Metastatic Castration-Resistant Prostate Cancer With Homologous Recombination Repair Gene Alterations: Final Analysis of the Asian Subgroup From the MAGNITUDE Study

Objectives: Patients with homologous recombination repair gene altered (HRR+) metastatic castration-resistant prostate cancer (mCRPC) have a poor prognosis but achieved clinical benefits when treated with first-line niraparib and abiraterone acetate plus prednisone (niraparib + AAP) in the MAGNITUDE trial. We report final exploratory results from MAGNITUDE for the subgroup of patients with Breast Cancer gene-positive (BRCA+) mCRPC enrolled in Asia (NCT03748641). Methods: Participants with HRR + mCRPC were randomized 1:1 to treatment with niraparib + AAP or placebo + AAP. The primary endpoint of radiographic progression-free survival (rPFS) by blinded independent central review (BICR) and secondary survival endpoints were calculated for the BRCA+ Asian subgroup. Safety was assessed in the Asian HRR+ population. Results: The Asian subgroup included 35 participants with BRCA + mCRPC (all BRCA2+). After 34.99 months of follow-up, median rPFS by BICR was 38.6 months in the niraparib + AAP group versus 8.3 months in the placebo+AAP group (hazard ratio [HR] 0.33, 95% confidence interval [CI] 0.13–0.83, nominal p-value = 0.0141). Clinically relevant benefits were also observed in time to PSA progression (HR 0.32, 95% CI 0.13–0.83), and time to cytotoxic chemotherapy (HR 0.098, 95% CI 0.01–0.68). Median overall survival was not reached in the niraparib+AAP group and was 24.0 months in the placebo+AAP group (HR 0.67, 95% CI 0.27–1.71). The safety profile of niraparib+AAP was consistent with the main study population. Conclusions: In this final exploratory analysis of the Asian subgroup, participants with BRCA + mCRPC continued to benefit from first-line treatment with niraparib + AAP in comparison to placebo + AAP, with efficacy and toxicity profiles consistent with the global study population. Trial Registration: United States National Library of Medicine (https://clinicaltrials.gov); NCT03748641.