Background: To explore the efficacy and safety of sintilimab plus regorafenib in refractory metastatic colorectal cancer (mCRC). Methods: We retrospectively evaluated the outcomes of the patients with mCRC who received at least one cycle of sintilimab plus regorafenib in the Hunan Cancer Hospital between July 2019 and June 2021. These patients had previously received at least two lines of standard chemotherapy including fluorouracil, oxaliplatin, and irinotecan with or without targeted drugs such as bevacizumab and cetuximab.The primary end point was overall survival (OS). Results: With a median follow-up of 6.00 months (range 0.70-22.47), the median overall survival (mOS) and progression-free survival (mPFS) were 9.00 months (95%CI: 5.00-NA) and 3.30 months (95%CI: 2.50-4.70).There was no significant difference in OS and PFS between patients with and without liver metastases,the mOS was 9.00 months 95%CI:[8.00-NA] vs 8.00months 95%CI:[5.00-NA]; P= 0.38, the mPFS was 3.87 months 95%CI:[3.10-13.70] vs 2.79 months 95%CI:[2.37-5.03]; P= 0.12.Cox multivariate regression analysis demonstrated that cycles of regorafenib plus PD-1 was a significant independent risk factor for the OS (P0.001),and it was a positive factor that there was just one metastatic site (P= 0.0038).Patients who had previously undergone surgery were better than those who had not (P= 0.0470).Seven patients got partial response and another 9 patients got stable disease in the 35 patients who were evaluated, but no complete response. Thus the objective response rate(ORR) was 20.0% and the disease control rate(DCR) was 45.7%.The incidence of grade 3/4 adverse evevts was 10.6%. Conclusions: The combination of sintilimab plus regorafenib had a manageable safety profile and promising efficacy in refractory mCRC patients. This combined therapy needs further prospective studies to verify the outcomes.

*Only 35 patients could be investigated for progression-free survival and response of the entire 66 patients.