Proposal of the minimal number of retrieved regional lymph nodes for accurate staging of distal bile duct cancer and clinical validation of the three-tier lymph node staging system (AJCC 8th edition)

Background: The minimal required number of retrieved lymph nodes (MNRLNs) to enable accurate staging of distal bile duct (DBD) adenocarcinoma remains unclear. The three-tier 8th N staging system of the American Joint Committee on Cancer (AJCC) for DBD adenocarcinoma has been recently released. The present study is aimed at proposing the MNRLNs for accurate staging and validating the 8th N stage. Methods: Between 1991 and 2015, patients with pathologically confirmed DBD adenocarcinoma who underwent pancreatoduodenectomy were enrolled. MNRLN was calculated via a log-rank test based on cut-off values. The concordance index (C-index) was utilized to compare the discrimination capability of the two- and three-tier N stages. Results: A total of 780 patients were enrolled. Lymph node (LN) positivity and 5-year overall survival (5-YOS) rates stabilized and significant survival differences between node-negative and –positive patients were observed when ≥12 LNs were retrieved. 5-YOS rates between each 8th N stage significantly differ (N0 vs. N1, P = 0.037; N1 vs. N2, P = 0.003). The C-index of the 8th N stage was higher than that of the 7th (0.59 vs. 0.57). Conclusions: For accurate staging, at least 12 LNs should be retrieved. The three-tier N staging system is valid for clinical practice and has a more accurate prognostic predictability than the two-tier system.