Clinical outcome of patients with germline DNA repair mutations: Results from a retrospective international study

218 Background: CRPC is enriched for germline mutations in DNA damage repair genes (gDDRm). BRCA2 mutations (g BRCA2m) associate with poor prognosis from localized PC, but prognostic and predictive value for standard therapy in CRPC is unclear. We reviewed clinical outcome of 390 patients previously tested for gDDRm. Methods: Patient records were reviewed for 372 patients from 3 institutions (Royal Marsden UK, Weill-Cornell NY, University of Washington, WA) with gDDRm status previously published (Pritchard et al, NEJM 2016) and 18 g BRCA1/2m carriers from KConFab consortium (Australia). Baseline characteristics and survival were annotated. Response (PSA50%/RECIST) and PFS (RECIST/PSA progression or start of a new therapy due to clinical progression) were collected for Abiraterone, Enzalutamide and Docetaxel. To account for potential differences between cohorts, a mixed effect model (Weibull distribution) with random intercept per cohort was pursued. Results: dDDRm status was available for n = 390 (60 gDDRm+, including 37 g BRCA2m, and 330 gDDRm-). Overall, 74% and 69% received Docetaxel and Abiraterone/Enzalutamide respectively; 47% gDDRm+ and 34% gDDRm- received PARPi and/or platinum. Median overall survival from CRPC was 3.0 vs 3.2 years in gDDRm+ vs gDDRm- (p = 0.73; g BRCA2m = 3.0 years, p = 0.72). Age and Gleason score at diagnosis were associated with survival from castration-resistance in multivariate analysis. Median PFS on Docetaxel for gDDRm+ (6.8 months; 6.3 for g BRCA2m) and gDDRm- (5.1 months) were not significantly different (p = 0.2). Similarly, RR to Docetaxel was similar for the two groups (61% vs 54% in gDDRm+ vs gDDRm-; 63% g BRCA2m). Median PFS and RR on first Abiraterone/Enzalutamide were similar across groups (PFS: 8.3 months gDDRm+, 8.3 months for gDDRm-; p = 0.9; RR 46% vs 56% respectively) The Interaction of PARPi/platinum therapy among gDDRm+ patients resulted in an aHR for OS from CRPC of 0.59 (95%CI 0.28-1.25; p = 0.17). Conclusions: In this retrospective analysis, CRPC patients with gDDRm still benefited from standard therapies similarly to non-mutation carriers; interpretation of survival data should consider the high proportion treated with PARPi/platinum.