Phenotypic differences related to homologous recombination repair (HRR) gene-mutated metastatic castration-resistant prostate cancer (mCRPC) treated in routine care settings in the United States (US).

Abstract

e17047 Background: Recent evidence suggests mutations in HRR genes predict clinical benefit from treatment with PARP inhibitors in patients (pts) with mCRPC. Little is known about the prevalence, clinical and prognostic phenotypes associated with HRR-mutated (HRRm) mCRPC pts receiving routine oncology care in the US. We assessed HRRm positivity rate and described difference in phenotypic factors between HRRm+ and HRRm- mCRPC patients receiving routine care in community oncology settings. Methods: In this retrospective cohort study, we identified biologically male pts with mCRPC, ≥18 years, who received HRRm testing and on systemic anti-cancer treatment from 5/1, 2020 – 3/31, 2022, from the Integra Connect database, an electronic medical record (EMR) and claims database of US cancer pts in community oncology. We defined 2 cohorts based on their HRRm status (defined by the presence of an alteration in at least 1 of the following genes: BRCA1/2, ATM, BARD1, BRIP1, CDK12, CHEK1, CHEK2, FANCL, PALB2, RAD51B, RAD51C, RAD51D, RAD54L). We described age and race (at diagnosis), cancer stage and Gleason score (at staging), and line of therapy (LOT), Eastern Cooperative Oncology Group (ECOG) performance status, prostate-specific antigen (PSA) values and microsatellite instability (MSI) status using values closest to mCRPC diagnosis. HRR tests were stratified by germline, ctDNA, and solid tumor. Results: The study cohort comprised 376 HRRm-tested pts: by ctDNA only – 29%, germline only – 16.2%, solid tissue only – 18.4% and > 2 testing types – 33.5%. 96 had HRRm+ mCRPC (25.5%). Median (IQR) age at diagnosis for both cohorts was 67 (43-89) years and there were no statistically significant differences in age, race, stage, Gleason score, PSA value, LOT or ECOG by HRRm status. HRRm+ rates by ctDNA, germline, and solid tissue testing were 26.6%, 13.1% and 21.7%, respectively. Of the 126 patients with > 2 testing types, HRRm+ rate was 30.9%. A higher, but not statistically significant, proportion of HRRm+ pts had Gleason scores 9-10 compared to HRRm- pts (54.8% vs 48.6%). Of HRRm- pts, 10.2% had MSI-H status compared to 6.5% in HRRm+ pts. Conclusions: In this real-world cohort of HRR gene-tested pts with mCRPC, we observed a 25.5% HRRm+ rate, which suggests the prevalence for HRR mutation is significant enough to warrant testing for all pts with mCRPC. Further research is needed to examine the impact of these findings on overall survival and other clinical outcomes.