Concept of Depth of Invasion can Improve Staging Performance in Patients with Resected Distal Cholangiocarcinoma: Validation of the American Joint Committee on Cancer Staging System

The American Joint Committee on Cancer (AJCC) staging system for distal cholangiocarcinoma (dCC) has evolved significantly. However, the prognostic correlation of the newly proposed staging system remains unclear. Therefore, we aimed to compare the staging performance between AJCC 7th and 8th editions for dCC. We reviewed pathological slides of consecutive patients who underwent resection for dCC between 2000 and 2022. According to the AJCC 8th edition, depth of invasion was defined as the distance from the basement membrane of adjacent normal or dysplastic epithelium to the deepest tumor invasion. We analyzed changes in the T category from the AJCC 7th to 8th edition and assessed overall survival and recurrence based on these staging systems. Among 428 patients, application of the 8th edition resulted in down-staging of 272 (63.6%) patients and up-staging of only 13 (3.0%). Lymph node metastases were identified in 150 (35.1%) patients, with 29 (6.8%) having ≥ 4 metastatic nodes. The C-indices for overall survival and recurrence are 0.557 and 0.569 for the T stage of the AJCC 7th edition, and 0.606 and 0.631 for that of the AJCC 8th edition (95% confidence interval for delta: 0.005-0.092 for survival, 0.023-0.100 for recurrence). Additionally, the T category of the 8th edition correlated more strongly with lymph node metastases than that of the 7th edition. In dCC, the T category of the AJCC 8th edition demonstrates improved prognostic correlation and better alignment with lymph node metastases compared to that of the 7th edition.