Presence of somatic/germline homologous recombination repair (HRR) mutations and outcomes in metastatic castration-resistant prostate cancer (mCRPC) patients (pts) receiving first-line (1L) treatment stratified by BRCA status.

Abstract

5003 Background: Understanding of the association between HRR mutations and outcomes in mCRPC pts is limited. This analysis investigated the prevalence and outcomes of pts with/out HRR mutations (somatic and/or germline), stratified as BRCA, non-BRCA, or HRR non-BRCA, who initiated 1L mCRPC treatment with novel hormonal therapy (NHT) or taxane. Methods: Eligible pts from PROREPAIR-B (NCT03075735), PROSENZA (NCT02922218), PROSTAC (NCT02362620), and PROSABI (NCT02787837) studies underwent paired somatic/germline DNA analyses using a custom NGS panel that included ATM, BRCA1, BRCA2, BRIP1, CDK12, CHEK2, FANCA, HDAC2, PALB2, RAD51B, and RAD54L. Those with pathogenic (likely) mutations in ≥1 allele of ≥1 gene were considered deficient (HRR). rPFS, PFS2, and OS were reported for BRCA, non-BRCA, and HRR non-BRCA subgroups; associations between mutations and outcomes were assessed using inverse probability weighted Cox models, which balanced the baseline (BL) characteristics between subgroups. Hazard ratios (HRs) with 95% confidence intervals (CIs) and p values are presented. Results: Of 729 pts, 223 (30.6%) were HRR, including 96 (13.2%) BRCA. 60.4% of pts were treated with NHT and 39.6% with taxane in 1L; 80.7% received at least second-line treatment. Median age at BL was 72.2 years, 63.5% had Gleason >7, 53.1% had ECOG ≥1, and 13.3% presented with visceral metastases. BL characteristics after adjustment were similar (standard mean difference: <0.1 in HRR and maximum 0.11 for all pts). BRCA pts had significantly worse rPFS, PFS2, and OS than non-BRCA pts; BRCA pts also had significantly worse PFS2 and OS than HRR non-BRCA pts. There were no significant differences between the outcomes of somatic and germline BRCA pts. Conclusions: BRCA pts, regardless of somatic/germline origin, had significantly worse rPFS, PFS2, and OS than the total non-BRCA population and significantly worse PFS2 and OS than non-BRCA pts in the HRR subgroup. It is crucial to screen early for HRR mutations, particularly in BRCA1/2, to begin timely, targeted mCRPC treatment and improve prognosis.[Table: see text]