Olaparib outcomes in metastatic castration-resistant prostate cancer: First real-world experience in safety and efficacy from the Chinese mainland

BACKGROUND: Olaparib, a poly (ADP-ribose) polymerase (PARP) inhibitor, has been approved for use in breast cancer susceptibility gene (BRCA)-mutated metastatic castration-resistant prostate cancer (mCPRC) patients. Our aim was to evaluate the adverse events (AEs) and efficacy of Olaparib in the treatment of mCRPC patients from the Chinese mainland. METHODS: We retrospectively included mCPRC patients treated with Olaparib more than for 28 days. Patients with alterations in 15 homologous recombination repair (HRR) genes were defined as the HRRmt group, and the rest were defined as the HRRwt group. The efficacy was analyzed by prostate-specific antigen (PSA) decreased rate and PSA progression-free survival (PFS). The partial response, good response, and high response of PSA were defined as a reduction of between 0% and 50%, greater than 50%, and greater than 90% from baseline. RESULTS: A total of 43 patients were enrolled in this study, including 26 HRRmt group patients and 17 HRRwt group patients. Two HRRwt patients received additional abiraterone therapy. A partial response, good response, and high response were achieved in 89% (23/26), 59% (15/26), and 15% (4/26) of HRRmt group patients, respectively. In HRRwt group, 59% (10/17), 35% (6/17), and 12% (2/17) of patients met the criteria of partial response, good response, and high response, respectively. Median PFS was 8.0 months in the HRRmt group and 3.0s months in the HRRwt group (HR, 0.61; 95% CI, 0.24–1.14; p = 0.148), respectively. All the 20 patients had AEs during Olaparib treatment. Ten episodes of grade 3 or 4 AEs were observed in four patients. The most common all-grade AEs were fatigue or asthenia (70%), anemia (65%), and decreased appetite (55%). CONCLUSIONS: Most of the AEs were tolerated, and Olaparib was effective in mCRPC patients with HRR deficiency. In addition, the underlying mechanism of the efficacy of Olaparib observed in HRRwt group patients remained explored.