Histological features of precancerous and early cancerous lesions of biliary tract carcinoma

Biliary tract carcinoma develops within the intrahepatic or extrahepatic biliary tree and gallbladder. Primary sclerosing cholangitis, hepatolithiasis, congenital choledochal cyst, liver fluke infection, pancreatobiliary maljunction, toxic exposures and hepatitis virus infection are risk factors for the development of human biliary carcinoma. The precise molecular abnormalities of biliary carcinogenesis are still unknown, but chronic inflammatory conditions induce the production of reactive oxygen or nitrogen species leading to DNA damage. Recent studies indicate that cholangiocarcinoma of the large bile duct may arise in premalignant lesions such as biliary intraepithelial neoplasm (BilIN) and intraductal papillary neoplasm of the bile duct (IPNB). BilIN and IPNB are generally confined to the large and septal‐sized bile duct. BilINs are occasionally observed in non‐biliary liver cirrhosis as well as chronic biliary disease. In contrast, the precursor lesion of intrahepatic cholangiocarcinoma of the small bile duct type remains unclear. We herein demonstrated the histological characteristics of different tumor development pathways from premalignant lesion to carcinoma in different sites of the biliary tree.