The finding, which comes from the TRITON3 clinical trial, provides evidence of clinical benefit for an indication for rucaparib that was granted an accelerated approval in May 2020.
“Rucaparib reduced the risk of progression or death by half in patients with BRCA alterations,” said lead author Alan H. Bryce, MD, medical director of the Genomic Oncology Clinic at Mayo Clinic Arizona, in Phoenix.
For the subgroup of patients with BRCA alterations, the median PFS was 11.2 months with rucaparib vs. 6.4 months (hazard ratio, 0.50; P < .001) among those who received physician’s choice of therapy, which included docetaxel or a second-generation ARPI, such as abiraterone or enzalutamide.
In another subgroup of patients whose disease had ATM alterations, the median PFS was 8.1 months with rucaparib vs. 6.8 months with physician’s choice of drug. The difference was not statistically significant.
However, the difference was significant in the intention-to-treat (ITT) population (comprising both subgroups), for whom the median PFS was 10.2 months with rucaparib vs. 6.4 months with physician’s choice of drug (HR, 0.61; P < .001 by log-rank test).
Dr. Bryce pointed out that three-quarters of the patients in the physician’s-choice arm who had progressive disease crossed over to rucaparib upon progression and that overall survival (OS) results are immature. At 62 months, median OS did not significantly differ in the BRCA subgroup (24.3 vs. 20.8 months favoring rucaparib; P = .21) or in the ITT group (23.6 vs. 20.9 months; P = .67).
Importantly, rucaparib was well tolerated. In all treatment groups, the most frequent adverse events were asthenia and fatigue, Bryce said. “There were no cases of myelodysplastic syndrome or acute myeloid leukemia reported.”
These results from the TRITON3 trial were presented at the 2023 ASCO Genitourinary Cancers Symposium and were published simultaneously in the New England Journal of Medicine.
Suggested benefit
Rucaparib is the first PARP inhibitor approved for use in patients with mCRPC that harbors deleterious BRCA mutations (germline and/or somatic) who have already been treated with androgen receptor–directed therapy and a taxane-based chemotherapy. This prostate cancer indication was granted an accelerated approval in May 2020 by the U.S. Food and Drug Administration on the basis of response rates and effect on levels of prostate-specific antigen (PSA) from the TRITON2 clinical trial, the forerunner of the current study.
The TRITON2 study was a single-arm clinical trial that involved three cohorts: 62 patients with a BRCA mutation (germline and/or somatic) and measurable disease; 115 patients with a BRCA mutation (germline and/or somatic) and measurable or nonmeasurable disease; and 209 patients with homologous recombination deficiency–positive mCRPC.
In an analysis of 115 patients with a deleterious BRCA mutation (germline and/or somatic) and measurable or nonmeasurable disease, the confirmed PSA response rate was 55%. For the patients with measurable disease and a BRCA mutation, the objective response rate was 44%. The objective response rate was similar for those with a germline BRCA mutation.
