Background: Anti-programmed death-1 (PD-1) antibodies have been shown to be effective in the treatment of dMMR CRC. We describe an updated analysis from a cohort of 19 patients (pts) with dMMR CRC treated with pembrolizumab. Methods: Pts were identified through review of the Mayo Clinic electronic medical record (EMR) and chemotherapy administration records from May 2015 through January 2017. All pts with dMMR CRC who received treatment with pembrolizumab were included. The EMR was reviewed to identify demographic, clinical, pathologic and treatment details. Overall survival (OS), progression free survival (PFS) and disease control rate (DCR = CR+PR+SD) are reported. Time to event analysis was calculated using the Kaplan-Meier method. Results: Nineteen pts were included in this analysis; median age at diagnosis was 48.6 years (range 25-93); 53% were female. Most primary tumors were right sided (n = 12; 63%), 6 (32%) were left sided and 1 (5%) was a tumor of unknown primary within the bowel. Twelve (63%) pts received ≥2 lines of therapy prior to pembrolizumab (range 1-4). Five pts received 2 mg/kg every 3 weeks, 11 received 200 mg/day every 3 weeks and 2 pts received 10 mg/kg (1 every 2 weeks, the other every 3 weeks). The most common alterations identified were loss of MLH1 (11/15) and PMS2 (12/15); 4 pts had germline mutations (mut) identified. KRAS mut was identified in 6/16 pts and 2 pts had BRAF mut. Three pts had MLH1 hypermethylation. Median number of cycles of pembrolizumab was 8 (range 1-35+), with 13 (68%) pts receiving ≥6 cycles. DCR at first assessment was 68%, with 5% CR, 47% PR and 16% SD. Median follow-up from diagnosis was 29 months (95% CI 18-42). Median OS was 103 months (95% CI 85-103); 12-month OS was 89%. Median OS from PD-1 therapy was 16.1 months (95% CI 16-NR); 12-month OS from PD-1 therapy was 79%. Median PFS was NR (95% CI 5-NR); 12-month PFS was 54%. At time of analysis, 9 pts remain on PD-1 therapy; 5 pts have died; 3 have received subsequent therapy. Conclusions: Anti-PD1 blockade with pembrolizumab can provide long lasting benefit in dMMR mCRC, even in heavily pretreated pts.