Immune checkpoint inhibitors (ICIs), such as anti-cytotoxic T lymphocyte-associated antigen 4 (anti-CTLA-4), anti-programmed cell death 1 (anti-PD-1), and anti-programmed death-ligand 1 (anti-PD-L1), have revolutionized the management of malignant tumors, especially those at advanced stages [1,2,3]. The gene discussed is PDCD1; the disease is cancer.