PDCD1 and mismatch repair cancer syndrome 1: MMR deficiency is found in only a small percentage of CRC patients [50], but patients with the MMR-deficient status (high level of somatic mutations) [51, 52] have been found to benefit from anti-PD-1/anti-PD-L1 treatment compared to their MMR-proficient counterparts due to the ability of the human immune system to recognize and neutralize the neoantigens produced as a result of MMR deficiency [5].