[Concept of perihilar cholangiocarcinoma in the General Rules for Clinical and Pathological Studies on Cancer of the Biliary Tract, 6th edition].

Hilar cholangiocarcinoma is clinically characterized by biliary obstruction in the porta hepatis. Because the boundary between the intrahepatic and extrahepatic bile duct is unclear, hilar cholangiocarcinoma can potentially arise from both ducts. Therefore, the definition of hilar cholangiocarcinoma remains under debate. In November 2013, the 6th edition of the General Rules for Clinical and Pathological Studies on Cancer of the Biliary Tract was released, following the American Joint Committee on Cancer (AJCC) or International Union Against Cancer (UICC) TNM system. In that edition, as an alternative to "hilar cholangiocarcinoma," the new term "perihilar cholangiocarcinoma" is defined as cholangiocarcinoma involving the perihilar bile duct, despite the presence or absence of a significant liver mass component. This definition clearly indicates that some intrahepatic as well as extrahepatic perihilar tumors are involved in the perihilar tumor category. From the clinical point of view, there is no need for a differential diagnosis between intrahepatic or extrahepatic tumors therefore, the new definition is readily applicable in multidisciplinary team management. Japanese clinicians were previously required to distinguish between the proper use of the AJCC/UICC and the Japanese staging systems, but now the current revision will allow the more convenient use of a single, globally standardized staging system in daily practice.