Immunophenotype profiling of various mucinous biliary tract cancers (BTCs) revealed that the gastro-intestinal phenotype (MUC2+, MUC5AC+, and MUC6+) was more prevalent in mucinous cystic neoplasms of the liver (MCN-L) and intraductal papillary mucinous neoplasms (IPMN) than in benign mucinous cystadenomas. Here, MUC5AC is linked to pancreatic intraductal papillary-mucinous neoplasm.