External validation study of the 8^th edition of the American Joint Committee on Cancer staging system for perihilar cholangiocarcinoma: a single-center experience in China and proposal for simplification

Background: Several changes have been made to the primary tumor (T) and lymph node (N) categories in the new 8^th edition of the American Joint Committee on Cancer (AJCC) staging system for perihilar cholangiocarcinoma (pCCA). This study was conducted to validate the 8^th edition of the AJCC staging system for pCCA in China.

Methods: A total of 335 patients who underwent curative-intent resection for pCCA between January 2010 and December 2018 were retrospectively enrolled. The overall survival (OS) of groups of patients was calculated using the Kaplan-Meier method. The log-rank test was used to compare OS between groups. The concordance index (C-index), Akaike information criteria (AIC), and time-dependent area under receiver operating characteristic (ROC) curve (AUC) were computed to evaluate the discriminatory power of the 8^th and 7^th editions of the AJCC staging system.

Results: The T category changed in 25 (7.5%) patients, the N category changed in 39 (11.6%) patients, and the tumor-node-metastasis (TNM) stage changed in 157 (46.9%) patients when the 8^th and 7^th editions were compared. No statistically significant difference in survival was observed between T2aN0M0 and T2bN0M0. The C-index of the 8^th edition was 0.609 [95% confidence interval (CI): 0.568-0.650], which was slightly higher than that of the 7^th edition (C-index, 0.599, 95% CI: 0.558-0.640). The time-dependent AUC value also corroborated that the 8^th edition had a better performance than the 7^th edition.

Conclusions: The 8^th edition of the AJCC staging system for pCCA showed a better ability than the 7^th edition to discriminate patient survival. However, further simplification of the 8^th edition is still needed.