PDCD1 and colorectal carcinoma: Immunotherapy, particularly inhibitors targeting immune checkpoints, including cytotoxic T-lymphocyte antigen-4 (CTLA4), programmed cell death protein 1 (PD-1), and programmed cell death 1 ligand 1 (PD-L1), has provided promising new therapy to improve the overall survival of patients with CRC [50,69,72].