Ongoing clinical trials in advanced biliary tract cancer patients reported that patients responded to ICI monotherapies with anti-programmed cell death ligand-1 (PD-L1), anti-programmed cell death protein-1 (PD-1), and anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) [28]. This evidence concerns the gene CTLA4 and biliary tract neoplasm.