(Chronic inflammation and infection of bile duct are the basis for the occurrence of bile duct cancer, because all diseases associated with bile duct cancer can lead to chronic inflammation of bile duct. Long-term stimulation of biliary tract mucosa by certain substances in bile (such as metabolites of bile acids) leads to epithelial atypical hyperplasia. 2.Bile duct and gallbladder stones 20%-57% of bile duct cancer patients are accompanied by gallstones, thus it is believed that chronic stimulation of stones may be a carcinogenic factor. 3.Ulcerative colitis has been reported that the incidence of bile duct cancer in patients with ulcerative colitis is 10 times higher than that of the general population. Patients with cholangiocarcinoma with ulcerative colitis have an earlier age of onset of 20-30 years than the general population, with an average age of 40-45 years, and often have a long-term history of colitis. Chronic bacteremia in the portal system of patients may be the cause of cholangiocarcinoma and PSC, and the lesions mostly affect the whole colon. 4.Cystic malformation of bile ducts (congenital bile duct dilatation) has become a consensus that congenital bile duct cysts are prone to cancer, and the incidence of bile duct cancer in patients with congenital bile duct cysts is as high as 2.5%~28%. Although 75% of bile duct cystic malformations show symptoms in infancy and childhood, as far as bile duct cancer is concerned, 3/4 of the patients are those who develop symptoms of bile duct cystic malformations in adulthood. Regarding the mechanism by which cystic malformation of the bile duct leads to bile duct cancer, it is believed that when the opening of the pancreatic duct into the bile duct is abnormally high, it can cause the reflux of pancreatic juice into the bile duct causing bile duct epithelial malignancy. Other factors that may lead to malignancy include bile stagnation, stone formation and chronic inflammation in the cystic lumen. Although Schistosoma haematobium is mostly parasitized in intrahepatic bile ducts, it can also be parasitized in extrahepatic bile ducts. The worm itself and its metabolites stimulate the bile duct mucosal epithelium for a long time, causing mucosal hyperplasia of bile ducts and producing tumor-like changes and carcinoma. 6.Cholangiocarcinoma of bile duct surgical history can occur years after surgery, and can occur in bile ducts without stones, mainly due to chronic bile duct infection leading to epithelial interstitial changes, often after bile duct internal drainage surgery. 7.The age of onset of bile duct cancer in patients with a history of exposure to radioactive thorium dioxide and thorium is 10 years earlier than in those without a history of thorium exposure, and its average latency is 35 years (after exposure to thorium), and it occurs more often at the end of the intrahepatic biliary tree. 8, sclerosing cholangitis malignant primary sclerosing cholangitis (PSC) patients also have a higher chance of developing bile duct cancer than the general population, PSC is also associated with ulcerative colitis. 9. Hepatitis B virus infection is associated with hepatitis B virus infection in some domestic patients with cholangiocarcinoma, whether there is a link between the two remains to be further elucidated. K-ras gene mutation In recent years, molecular biology research shows that the rate of K-ras gene 12 codon mutation in cholangiocarcinoma reaches 77.4%, which indicates that K-ras gene mutation may play a more important role in the occurrence of cholangiocarcinoma. In addition, it may be associated with pancreatic reflux, biliary stasis, stone formation, malignant transformation of benign bile duct tumors, and tumor-like differentiation of liver stem cells. All of them can cause chronic inflammatory irritation to the bile duct mucosa, which in turn can induce bile duct cancer. (II) Pathogenesis Cholangiocarcinoma can occur in various parts of extrahepatic bile ducts, among which proximal bile duct (hilar bile duct) is the most common, accounting for about 58%; middle and distal bile ducts account for 13% and 18% respectively (Figure 1), 4% occur in the biliary cystic duct, and another 7% occur diffusely. 1. Pathological features (1) morphological classification: according to the general morphology of tumor, bile duct cancer can be divided into four types: papillary type, sclerotic type, nodular type and diffuse infiltrative type. Among them, infiltrating type is more common, followed by nodular type, while papillary type is less common. Bile duct cancer is generally less likely to form masses and more likely to be infiltrated, thickened and occluded by the duct wall; the cancerous tissues tend to infiltrate into the surrounding tissues and often invade the nerves and liver; patients often die from intrahepatic and biliary tract infection. (2) Histological classification: more than 95% of cholangiocarcinoma are adenocarcinoma, a few are squamous epithelial carcinoma, mucinous carcinoma, cystic adenocarcinoma, etc. Among primary extrahepatic cholangiocarcinoma, common bile duct carcinoma is the most common, 33%-40%; followed by common hepatic duct carcinoma, 30%-32%; common hepatic duct bifurcation, 20%; bile cyst duct 4%.