In SE Asia, where the tumour is quite common, the associated risk factors are: - liver flukes-Opisthorchis viverrini and Clonorchis sinensis, - chronic typhoid carriers-sixfold increased risk of all hepatobiliary malignancy. 2.2 Anatomical classification 3- 5 "Cholangiocarcinoma" originally referred only to primary tumours of the intrahepatic bile ducts and was not used for extrahepatic bile duct tumours but the term is now regarded as inclusive of intrahepatic, perihilar, and distal extrahepatic tumours of the bile ducts (fig 1). The WHO classifications are given below. 2.3.1 WHO classification of carcinomas of the liver Hepatocellular carcinoma Combined hepatocellular cholangiocarcinoma Cholangiocarcinoma, intrahepatic Bile duct cystadenocarcinoma Undifferentiated carcinoma 2.3.2 WHO classification of carcinomas of the extrahepatic bile ducts Carcinoma in situ Adenocarcinoma Papillary adenocarcinoma Adenocarcinoma, intestinal-type Mucinous adenocarcinoma Clear cell adenocarcinoma Signet ring cell carcinoma Adenosquamous carcinoma Squamous cell carcinoma Small cell carcinoma (oat cell carcinoma) Undifferentiated carcinoma 2.3.3 Histological grade Most cholangiocarcinomas (95%) are adenocarcinomas.