An malignant tumor composed of cells resembling those of bile ducts. Cholangiocarcinoma is a relatively rare tumor in most populations. It can arise from any portion of the intrahepatic bile duct epithelium or the hepatic ducts. Grossly, the lesions are nodular, grayish-white firm and solid. Microscopically, the vast majority of cholangiocarcinomas are adenocarcinomas showing tubular and/or papillary structures. Early detection of cholangiocarcinomas is difficult, and the overall prognosis after resection is poor (adapted from WHO, 2000). --2002