PDCD1 and cancer: Thus, cancer immunotherapy targeting proteins including programmed cell death-1 (PD-1) and programmed cell death ligand-1 (PD-L1), lymphocyte activation gene 3 (LAG-3), and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), proved to be effective in different types of cancers [16,17,18].