Immune checkpoint inhibitors targeting cytotoxic T lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD1), and programmed cell death ligand 1 (PD-L1) have been approved by the United States Food and Drug Administration (FDA) and are considered promising systemic therapies based on clinical trials for various types of cancers [1]. The gene discussed is PDCD1; the disease is cancer.