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

To propose a shared T classification system for biliary cancers located around the cystic duct junction.

These cancers include perihilar cholangiocarcinoma (PCC), distal cholangiocarcinoma (DCC), and cystic duct carcinoma (CDC), which are staged according to discrete tumor classification.

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.

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.

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.