Programmed cell death 1 (PD-1) and cytotoxic T lymphocyte antigen 4 (CTLA-4) are co-inhibitory receptors expressed on the surface of T cells to negatively regulate T cell-mediated immune responses; however, tumour cells exploit these inhibitory molecules in order to induce tumour tolerance and T cell exhaustion [2]. This evidence concerns the gene PDCD1 and neoplasm.