DNA damage and repair (DDR) gene variants and outcomes in localized and metastatic prostate cancer (mPC).

Abstract

304 Background: Moderate frequencies of DDR gene variants exist in mPC. Their prognostic role in localized and mPC is unclear. This study aims to characterize DDR variants in a cohort of hormone sensitive localized and mPC and assess for association with outcome. Methods: A retrospective cohort of men with PC and ≥ 2 follow up visits at DFCI and targeted next generation sequencing of prostate or metastatic tissue was identified. Biomarker (BM) positive was defined as pathogenic changes in the following DDR genes: ATM BAP1 BRCA1 BRCA2 BRIP1 CHEK2 MSH2 MSH6 PALB2 PMS2. For localized PC, outcome endpoints included event-free survival (EFS) (time from prostate biopsy to PSA relapse/metastasis/death), metastasis-free survival (MFS) (time to metastasis/death), time to castration resistance (CRPC), and death (OS); for mPC, outcome events included time from androgen deprivation start to CRPC and OS. BM status was descriptively summarized. Kaplan-Meier method and Cox regression model assessed associations of BM status with clinical outcomes. Results: Of the 237 men included, 16 (7%) were BM positive; 12 (6%) in 205 localized PC, 6 (14%) in 43 mPC. BM positive genes included 9 (4%) ATM, 6 (3%) BRCA2, and 2 (0.8%) CHEK2. In men with localized PC, EFS events occurred in 58% (7/12) BM positive vs 34% (66/193) BM negative at median follow up of 3.1 years; BM positive trended toward a shorter EFS (median 1.9 vs 5 years) than BM negative (HR 2.17, 95%CI 0.99-4.76). MFS events were observed in 17% (2/12) BM positive vs 7% (15/193) BM negative. CRPC events occurred in 17% (2/12) BM positive vs 6% (11/193) BM negative. In men with mPC, there were CRPC events in 100% (6/6) BM positive vs 67% (25/37) BM negative at median follow up of 3.3 years; BM positive trended toward a shorter time to CRPC (median 4 vs 8.8 months) compared to BM negative (HR 1.87, 95%CI 0.76-4.64). There was no association between BM status and OS. Conclusions: DDR variants appear infrequently in localized PC but may portend a shorter time to PSA relapse and metastasis. Similarly, DDR variants in mPC may be associated with a shorter time to CRPC. Low frequency of variants and short follow up limit these analyses. The prognostic value of DDR variants remains unclear and requires further research.