New Tumor Classification Using Invasion Depth in Biliary Tract Cancer Around the Cystic Duct Junction

Objective: To propose a shared T classification system for biliary cancers located around the cystic duct junction. Summary Background Data: These cancers include perihilar cholangiocarcinoma (PCC), distal cholangiocarcinoma (DCC), and cystic duct carcinoma (CDC), which are staged according to discrete tumor classification. Methods: From 2011 to 2019, patients with biliary cancers that clinically invaded the junction (junctional cholangiocarcinoma [JCC] ) were classified as having PCC, DCC, CDC, or unclassifiable tumor (UT) based on topologic predominance. The prognostic stratifying ability of the specific American Joint Committee on Cancer T system and depth-based classification were compared between patients with JCC and UT. Results: Among 191 patients with JCC, 63, 20, and 20 had PCC, DCC, and CDC, respectively; the remaining 88 (46%) had UT. The DCC group showed a better survival rate of 70% at 5 years than the other groups (48% for UT, 36% for PCC, and 29% for CDC). Specific tumor classifications of PCC, DCC, and CDC significantly stratified survival in 88 patients with UT, with c-indices of 0.611, 0.613, and 0.563, respectively. Stratified by depth-based classification (T1, ≤1 mm; T2, >1-5; T3, 6-10; and T4, >10 mm), the 5-year survival rates were 83%, 67%, 44%, and 0% in the UT cohort ( P <0.001, C-index, 0.654) and 88%, 60%, 41%, and 24% in the entire JCC cohort ( P <0.001, C-index, 0.632), respectively. Conclusions: The depth-based T classification significantly stratified survival in the clinical category of JCC and histologically defined UT. Cholangiocarcinoma and CDC in this region can be grouped under the banner of the JCC.