Notably, the recent success of immune checkpoint blockade in cancer therapy illustrates the importance of two inhibitory pathways, cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), and programmed cell death protein 1 (PD1) and its ligands (PD-L1, PD-L2), in the regulation of anti-tumor immune responses. This evidence concerns the gene PDCD1 and neoplasm.