MSH6 and colorectal carcinoma: Since some patients with microsatellite-instability-high (MSI-H) or mismatch repair-deficient (dMMR) CRC appear to be susceptible to PD-1/PD-L1 blockade,21 we also detected the expression of mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2) in CRC tissues (Supplementary Fig. S1a).