Immune checkpoint inhibitor (ICI) therapy is a type of cancer immunotherapy that works through suppression of immune inhibitory pathways such as the programmed cell death protein-1 (PD-1)/programmed death-ligand-1 (PD-L1) axis and the cytotoxic lymphocytes antigen proteins (CTLA-4) pathway [1]. The gene discussed is PDCD1; the disease is cancer.