Classification of Intrahepatic Cholangiocarcinoma into Perihilar Versus Peripheral Subtype.

BACKGROUND: Intrahepatic cholangiocarcinoma (ICC) constitutes a group of heterogeneous malignancies within the liver. We sought to subtype ICC based on anatomical origin of tumors, as well as propose modifications of the current classification system. METHODS: Patients undergoing curative-intent resection for ICC, hilar cholangiocarcinoma (CCA), or hepatocellular carcinoma (HCC) were identified from three international multi-institutional consortia of databases. Clinicopathological characteristics and survival outcomes were assessed. RESULTS: Among 1264 patients with ICC, 1066 (84.3%) were classified as ICC-peripheral subtype, whereas 198 (15.7%) were categorized as ICC-perihilar subtype. Compared with ICC-peripheral subtype, ICC-perihilar subtype was more often associated with aggressive tumor characteristics, including a higher incidence of nodal metastasis, macro- and microvascular invasion, perineural invasion, as well as worse overall survival (OS) (median: ICC-perihilar 19.8 vs. ICC-peripheral 37.1 months; p < 0.001) and disease-free survival (DFS) (median: ICC-perihilar 12.8 vs. ICC-peripheral 15.2 months; p = 0.019). ICC-perihilar subtype and hilar CCA had comparable OS (19.8 vs. 21.4 months; p = 0.581) and DFS (12.8 vs. 16.8 months; p = 0.140). ICC-peripheral subtype tumors were associated with more advanced tumor features, as well as worse survival outcomes versus HCC (OS, median: ICC-peripheral 37.1 vs. HCC 74.3 months; p < 0.001; DFS, median: ICC-peripheral 15.2 vs. HCC 45.5 months; p < 0.001). CONCLUSIONS: ICC should be classified as ICC-perihilar and ICC-peripheral subtype based on distinct clinicopathological features and survival outcomes. ICC-perihilar subtype behaved more like carcinoma of the bile duct (i.e., hilar CCA), whereas ICC-peripheral subtype had features and a prognosis more akin to a primary liver malignancy.