A cholangiocarcinoma that arises from the junction, or adjacent to the junction, of the right and left hepatic ducts. The disease is hilar cholangiocarcinoma (MONDO_0003345, a Monarch Disease Ontology id). Also known as: Klatskin tumor, Klatskin tumour, Klatskin's tumor, Klatskin's tumour, cholangiocarcinoma of hilar portion of hepatic duct, hilar CC, hilar CCA, hilar portion of hepatic duct cholangiocarcinoma.