In a recent systematic review of the efficacy of anti-PD-1/PD-L1 monotherapy across 31 tumor types, Mao et al. [38] reported the highest ORR in mismatch repair-deficient colorectal cancer (ORR 38.8%) and mucosal melanoma (ORR 37.0%), while in germ cell tumors the ORR was 0%. Here, PDCD1 is linked to colorectal cancer.