PDCD1 and neoplasm: The main immune‐checkpoint inhibitors target cytotoxic T‐lymphocyte associated antigen 4 (CTLA‐4) and programmed cell death protein 1 (PD‐1)/PD1 ligand 1 (PD‐L1).23 CTLA‐4 can be expressed by regulatory T cells infiltrating tumor lesions, and it mediates immunosuppression by inhibiting T‐cell functions.