PDCD1 and cancer: However, only a subset of patients with these types of cancer showed durable clinical responses (4, 5), and numerous other types of cancer, among which MMR-proficient CRC, are resistant to anti-PD-1/PD-L1 therapies (6, 7), suggesting that in these patients mechanisms are present that limit the effects of anti-PD-1/PD-L1 antibodies.