Background: DDR-a are prevalent in mPC pts. The clinical behaviour of these pts is not well defined. We sought to investigate how DDR-a affects prognosis and treatment outcomes in mPC pts. Methods: Eligible pts were age ≥18 with mPC who had undergone germline (G) and/or somatic (S) next generation sequencing (NGS) at the Cross Cancer Institute 2016-2021. Pts were considered DDR-a if a pathogenic/likely pathogenic variant (P/LP-v) in a DDR gene was identified on G or S NGS; patients were considered DDR-p if no P/LP-v was identified on S NGS. Data from electronic medical records were collected. The primary endpoint was overall survival (OS) from diagnosis of mPC. Secondary endpoints included: OS and progression free survival (PFS) from initial diagnosis of prostate cancer (PC); PSA response after 12 weeks, and PFS and OS from the start time of 1st and 2nd line therapies. Time based endpoints were analyzed using the Kaplan-Meier (KM) method, and log-rank statistics were used to compare the KM curves. PSA responses were compared using chi-squared testing. Results: 23 DDR-a and 48 DDR-p pts were identified. The most frequent DDR-a were BRCA2 (n=11) and ATM (n=6). Baseline characteristics including age at diagnosis were similar between the two groups. 1st line systemic therapy was androgen deprivation therapy (ADT) alone in 73.9% of DDR-a and 77.0% of DDR-p. 2nd line therapy was abiraterone or enzalutamide in 65% of DDR-a and 92% of DDR-p. Olaparib was received by 52% of DDR-a pts. No difference in OS from mPC (65.7 vs 51.0 mos, p=0.487), OS from initial diagnosis (94.1 vs 88.9 mos, p=0.865), PFS on 1st line therapy (33.2 vs 31.0 mos, p=0.847), OS on 1st line therapy (85.6 vs 78.6 mos, (p=0.799) PFS on 2nd line therapy (8.4 vs 13.1 mos, p=0.569) or OS on 2nd line therapy (32.5 vs 35.8 mos, p=0.901) was seen for DDR-a vs DDR-p, respectively. PSA responses to 1st and 2nd line therapies were similar and will be presented as waterfall plots. Conclusions: In this single-center cohort, no difference in clinical characteristics or outcomes were seen in DDR-a compared to DDR-p pts. While this study is limited by small numbers and retrospective nature, it adds to the growing literature characterizing the clinical behaviour of DDR-a mPC. Collaborative efforts are required to better define this molecular cohort of pts.