It is known that immune checkpoints, including programed cell death protein 1 (PD-1), programed cell death ligand 1 (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), can suppress the T-cell-mediated immune responses, which permits cancer cells to escape from the immune destruction (10). This evidence concerns the gene PDCD1 and cancer.