235 Background: Mutations in BRCA 1/2 are typically associated with breast, ovarian, pancreatic and prostate cancers. BRCA mutations have been reported in colorectal cancer in sporadic case series. Unlike other cancers, the significance of BRCA mutations in mCRC is not known. We report the prevalence and molecular characteristics associated with BRCA 1/2 mutations in mCRC, and investigate the impact of these mutations on chemotherapy response since both oxaliplatin (OX) and irinotecan (IRI) interfere with DNA repair pathways. Methods: The Ontario-wide Cancer Targeted Nucleic Acid Evaluation (OCTANE) database was queried to identify mCRC patients (pts) harbouring BRCA 1/2 mutations. BRCA 1/2 mutations were detected using panel-based next generation sequencing (NGS) on archival tumour tissue. Clinical and molecular variables were collected, together with treatment outcomes. Results: Of 279 mCRC pts within the OCTANE database as of March 2019, 9 pts with BRCA 1/2 mutations were identified (3.2%): 4 BRCA 1 and 5 BRCA 2 mutations. Each patient had a unique variant with 8/9 missense mutations and 1/9 splicing error. Allele frequency ranged from 0.11 to 0.57. RAS or BRAF mutations were present in 67%. Common co-mutations included TP53 (56%), APC (56%), TSC1 (44%), ROS1 (33%) and ATM(33%). 2 pts were mismatch repair deficient. Median age was 48.5 years (range: 31-69 years), 56% males. 5 pts presented with de novo metastatic disease. First line OX-containing chemotherapy was administered to 4 pts, and IRI to 3 pts. 2 pts did not receive chemotherapy (1 had surgery only post-adjuvant OX, and 1 immunotherapy). Overall response rate (ORR) was 71%, with all pts achieving a partial response or stable disease. The median progression-free survival was 7.5 months (range: 1.8- 31.7 months) and median overall survival 68.5 months (range: 10.5- 68.5 months) respectively. Conclusions: BRCA 1/2 mutations are present in a small subset of mCRC pts. Pts with these mutations tend to be younger at diagnosis. BRCA 1/2 mutations are associated with favourable response to first line chemotherapy. Targeting BRCA 1/2 mutations may broaden treatment options for these patients.