PDCD1 and cancer: Several cancer-related inhibitory immunoreceptors related to cancer have been identified, including PD-1 (programmed cell death protein 1), CTLA-4 (T lymphocyte-associated antigen), LAG-3 (lymphocyte-activation gene 3), TIM-3 (T cell immunoglobulin domain and mucin domain-3), TIGIT(T cell immune receptor with immunoglobulin and ITIM domain), and BTLA (B and T lymphocyte attenuator) [133].