In recent years, with the discovery of tumor immune checkpoint molecules, such as cytotoxic T lymphocyte (CTL)-associated protein-4 (CTLA-4), programmed cell death protein-1 (PD-1), and its ligand PD-L1, important breakthroughs have been made in the study of antitumor immune mechanisms, and immunotherapy has become a promising tumor treatment (17, 18). Here, PDCD1 is linked to neoplasm.