PDCD1 and colorectal carcinoma: Despite initial studies of ICB in CRC had given disappointing results [176,177,178], the stratification by TMB and immune infiltrate has highlighted the efficacy of PD-1 and CTLA4 neutralization in a small subgroup of CRC patients characterized by an MSI-H phenotype due to a deficient DNA mismatch repair (dMMR) system [179,180,181].