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]. Here, PDCD1 is linked to biliary tract cancer.