MUC5AC and cholangiocarcinoma: Histological pCCA and dCCA are invariably pure-mucin secreting adenocarcinoma, while, IH-CCA includes two different subtypes, a mucin-IHCCA similar to pCCA and a mixed-IHCCA in which areas of hepatocytic differentiation and neoplastic ductular reaction are also included within the tumor mass The two different subtypes of IHCCA likely originated from different cells, specifically the mucin-secreting epithelial cells lining large ducts and peribiliary glands in mucin-IHCCA, or the cuboidal non-mucin-secreting cells lining bile ductules or canals of Hering in mixed-IHCCA [2,3].