Cholangiocarcinoma is a primary cancer originating in the biliary epithelium i.e., the cholangiocytes, of the extrahepatic and intrahepatic biliary ducts. It is extremely invasive, develops rapidly, often metastasizes, and has a very poor prognosis. They are slow growing tumors which spread longitudinally along the bile ducts with neural, perineural and subepithelial extension. [https://orcid.org/0000-0002-0736-9199, PMID:18536057, PMID:8268770]
