Risk factors for biliary tract carcinogenesis.
Cholangiocarcinoma has a worldwide distribution which accounts for about 10-15% of all cases of primary hepatobiliary malignancy. Although, in the majority of cases, no aetiological factor can be identified, a number of risk factors have been shown to be important in the development of cholangiocarcinoma; most of these factors share long standing inflammation and chronic injury of the biliary epithelium. Primary sclerosing cholangitis is an uncommon disease, characterized by stricturing, fibrosis and inflammation of the biliary tree which is closely associated with chronic inflammatory bowel disease, particularly ulcerative colitis. It is commonly associated with cholangiocarcinoma and between 10-20% of patients with primary sclerosing cholangitis will go on to develop a cholangiocarcinoma. The rare congenital fibropolycystic diseases of the biliary system are associated with increased risks of cholangiocarcinoma, particularly choledochal cysts and Caroli's disease. Choledochal cysts are associated with a 10% overall incidence of cholangiocarcinoma: there is a 1% cumulative risk which plateaus after 15-20 years. However, the risk is diminished in children who present under the age of 10 years where the over all risk is 0.7%. This compares with the 14% over all risk of patients presenting over the age of 20 years. In the Far East, other forms of chronic inflammation associated with cholangiocarcinoma include infestation with liver flukes. Clonorchis sinensis and Opisthorchis viverinni. Cholangiocarcinoma is also rarely seen in association with cirrhosis and has been weakly linked to hepatitis C infection.