Perihilar (hilar) bile duct cancers (those starting in the hilum, the area just outside the liver) Distal bile duct cancers (those starting farther down the bile duct system) Nearly all bile duct cancers start in the innermost layer of the wall of the bile duct, called the mucosa. Over time they can grow through the wall toward the outside of …
https://www.cancer.org/cancer/bile-duct-cancer/detection-diagnosis-staging/staging.html

