PDCD1 and cancer: Immune checkpoint inhibitors (ICIs), such as anti‐cytotoxic T lymphocyte antigen 4 (CTLA‐4) and anti‐programmed cell death 1 (PD‐1)/programmed cell death‐ligand 1 (PD‐L1) monoclonal antibodies, block the interactions between cancer cells and the immune system to enhance immune response to the tumor by rebalancing immune surveillance and immune evasion.