Pancreatic Cancer Lymph Node Resection Revisited: A Novel Calculation of Number of Lymph Nodes Required

Background: Pancreatic cancer is the third leading cause of cancer related deaths in the US. Although lymph node (LN) metastasis is a prognostic indicator, the extent of LN resection is still debated. Our goal was to use the distribution of the ratio of positive to negative LNs to derive a more adequate number of necessary examined LNs based on the target LN threshold (TLNT). Study Design: Using the National Cancer Database, we performed a retrospective study of surgically resected pancreatic adenocarcinoma (2010 to 2015). We evaluated the number of positive LNs and total LNs examined and the log of the ratio of positive LNs to negative LNs (LODDS). The distribution of LODDS was examined to determine a target LNs examined threshold sufficient to detect N1 disease. Using the LODDS distribution of N1 cases, target LNs examined threshold were calculated to encompass 90 of the N1 group distribution. Results: Of the total 24,038 resected patients included in this study, 26% underwent operation only, 18% received neoadjuvant therapy, and 56% underwent adjuvant therapy. In all, 8,144 (34%) patients had N0 disease and 15,894 (66%) had N1 disease. To capture 90% to 95% of the N1 group, the minimum number of LNs examined would be 18 (LODDS −2.74) to 24 (LODDS −3.04), respectively. Conclusions: Although previous studies have suggested 11 to 17 LNs required for adequate LN sampling in pancreatic cancer, our findings suggest that to capture 90% of cases with N1 disease, 18 LNs is more appropriate.