Immune checkpoint inhibitors (ICIs) that target the T-cell inhibitory checkpoint proteins CTLA-4, PD-1, or the PD-1 ligand PD-L1 have been approved for the treatment of a variety of cancers, including melanoma, non-small-cell lung cancer, head–neck cancer, bladder cancer, renal cell cancer, hepatocellular carcinoma (HCC), and several other tumor types. The gene discussed is CTLA4; the disease is hepatocellular carcinoma.