MUC5AC and biliary tract cancer: The safety, toxicity, tolerance, and anti-tumor efficacy of peptide vaccines, such as Wilms tumor 1 (WT1) peptide vaccine (97, 113), mucin 1 (MUC1) peptide vaccine (98), mucin 5AC (MUC5AC) peptide vaccine (97), and carcinoembryonic antigen (CEA) peptide vaccine (97), were verified in phase I clinical trials against advanced biliary tract cancers.