PDCD1 and neoplasm: Immune checkpoint blockade (ICB) has progressed most prominently as an effective immunotherapy by targeting inhibitory T cell regulatory molecules such as programmed cell death-1 (PD-1), its ligands programmed cell death ligand 1/2 (PD-L1/L2), and cytotoxic T-lymphocyte associated antigen-4 (CTLA-4), thereby re-invigorating the anti-tumor immune response (8).