Given the dramatic therapeutic response of the patients with high PD-L1 expression in our study, and the fact PD-L1 IHC is considered a cost-effective screening tool for routine usage in the clinic, PD-L1 could serve as an alternative predictive biomarker for pembrolizumab immunotherapy in advanced biliary tract cancers refractory to standard chemotherapy. Here, CD274 is linked to biliary tract cancer.