Avalumab is an anti-PD-L1 antibody recently tested in several different types of tumors with promising results and is currently being studied in phase III in gastric cancer. There is no data on the effectiveness of this ICI in the MSI mCRCs. In addition, only anti-PD1 was used in the MSI-mCRC and not the anti-PD-L1, and only in chemoresistance (3rd line or more). The main objective of the SAMCO study is to test the efficacy and tolerance of avelumab in the 2nd line of treatment in patients with a MSI mCRC progression after standard 1st line chemotherapy +/- targeted therapy.