Defining the Minimal and Optimal Thresholds for Lymph Node Resection and Examination for Intraductal Papillary Mucinous Neoplasm Derived Pancreatic Cancer

Objective: To establish minimal and optimal lymphadenectomy thresholds for intraductal papillary mucinous neoplasm (IPMN)-derived pancreatic ductal adenocarcinoma (PDAC) and evaluate their prognostic value. Background: Current guidelines recommend a minimum of 12-15 lymph nodes (LNs) in PDAC. This is largely based on pancreatic intraepithelial neoplasia (PanIN)-derived PDAC, a biologically distinct entity from IPMN-derived PDAC. Methods: Multicenter retrospective study including consecutive patients undergoing upfront surgery for IPMN-derived PDAC was conducted. The minimum cut-off for lymphadenectomy was defined as the maximum number of LNs where a significant node positivity difference was observed. Maximally selected log-rank statistic was used to derive the optimal lymphadenectomy cut-off (maximize survival). Kaplan-Meier curves and log-rank tests were used to analyze overall survival (OS) and recurrence-free survival (RFS). Multivariable Cox-regression was used to determine hazard ratios (HR) with 95% confidence intervals (95%CI). Results: In 341 patients with resected IPMN-derived PDAC, the minimum number of LNs needed to ensure accurate nodal staging was 10 ( P =0.040), whereas ≥20 LNs was the optimal number associated with improved OS (80.3 vs. 37.2 mo, P <0.001). Optimal lymphadenectomy was associated with improved OS [HR:0.57 (95%CI 0.39-0.83)] and RFS [HR:0.70 (95%CI 0.51-0.97)] on multivariable Cox-regression. On sub-analysis the optimal lymphadenectomy cut-offs for pancreatoduodenectomy, distal pancreatectomy, and total pancreatectomy were 20 ( P <0.001), 23 ( P =0.160), and 25 ( P =0.008). Conclusion: In IPMN-derived PDAC, lymphadenectomy with at least 10 lymph nodes mitigates under-staging, and at least 20 lymph nodes is associated with the improved survival. Specifically, for pancreatoduodenectomy and total pancreatectomy, 20 and 25 lymph nodes were the optimal cut-offs.