PDCD1 and neoplasm: Tumor cells are capable of hijacking the patients’ T cell immune checkpoints, such as cytotoxic T-lymphocyte associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1), which act as negative regulators of immune response by surface expression of members of the B7 family of immune-regulatory ligands and B7 homologs such as programmed cell death ligand 1 (PD-L1) and programmed cell death ligand 1 (PD-L2) [9,10,11] (Figure 1a).