PDCD1 and cancer: In recent decades, several inhibitory immunoreceptors including programmed cell death protein 1 (PD-1) and its ligand (PD-L1), cytotoxic T-lymphocyte protein 4 (CTLA-4), lymphocyte-activation gene 3 (LAG3), T cell immunoglobulin and mucin-domain containing-3 (TIM3), T cell immunoreceptor with Ig and ITIM domains (TIGIT), and B- and T-lymphocyte attenuator (BTLA) have been identified and evaluated in various cancers.