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Bile duct cancer is a malignant tumour that starts in the cells of a bile duct. Malignant means that it can spread, or metastasize, to other parts of the body.
The bile ducts are part of the digestive system. Bile is a yellow-green fluid that helps your body digest fats. The bile ducts are tubes that carry bile from the liver to the duodenum, which is the first part of the small intestine. The 2 ducts that start inside the liver are called the hepatic ducts. They leave the liver and join to form the common hepatic duct. The common hepatic duct joins the cystic duct that leaves the gallbladder to form the common bile duct.
Cells in a bile duct sometimes change and no longer grow or behave normally. In some cases, changes to bile duct cells can cause cancer. Bile duct cancers are grouped and treated based mainly on if they start inside or outside of the liver.
Most bile duct cancers begin in a bile duct outside of the liver. Cancers that start in these structures are called extrahepatic bile duct cancer. They can start in a hepatic bile duct outside of the liver or the common bile duct. Over 90% of extrahepatic bile duct cancers start in gland cells that line the inside of a bile duct. This type of cancer is called adenocarcinoma of the bile duct.
Other types of cancer can also start in the bile ducts outside of the liver, but they are rare. These include signet-ring cell carcinoma and clear cell carcinoma.
Bile duct cancer that starts in a hepatic bile duct inside the liver is called intrahepatic bile duct cancer. This type of cancer may also be called intrahepatic cholangiocarcinoma, or ICC. (The term cholangiocarcinoma may be used to describe both intrahepatic and extrahepatic bile duct cancer, but it is more commonly used for intrahepatic bile duct cancer.)
Intrahepatic bile duct cancer makes up 5%–10% of all bile duct cancers. It is less common than extrahepatic bile duct cancer.