PDCD1 and liver cancer: In the context of immunotherapy, whether a patient’s liver cancer cells highly express cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), programmed cell death protein-1 (PD1), programmed cell death ligand 1 (PD-L1), or other immune checkpoint genes that prevent immune cells from functioning is key to whether treatment with antibodies is likely to be effective [7].