Lymphovascular Invasion Predicts Lymph Node Involvement in Small Pancreatic Neuroendocrine Tumors

Introduction: Pancreatic neuroendocrine tumors (p-NETS) are increasing in incidence, and prognostic factors continue to evolve. The benefit of lymphadenectomy for p-NETS ≤2 cm remains unclear. We sought to determine the significance of lymphovascular invasion (LVI) for small p-NETS. Methods: The National Cancer Database was queried for patients with p-NETS ≤2 cm and with ≥1 evaluated lymph node (LN), years 2004-2015. Demographic, clinical, and treatment characteristics were analyzed. Multivariate logistic regression was performed to identify predictors of LN positivity. Results: Among 2,499 patients identified, tumor location was delineated as the head (26%), body (18%), tail (38%), or unspecified (18%); 74% were well-differentiated versus 10% moderate, 2% poor, and 14% unknown. LVI occurred in 11%. A median of 9 LNs were evaluated; overall positivity was 18%. Mean survival was significantly longer in node-negative patients (115 vs. 95 months, log-rank p < 0.0001). LVI was the strongest predictor of node involvement (OR 10.4, p < 0.0001) when controlling for tumor size, grade, and location. Subset analysis of patients with known LVI status, grade, location, and mitoses found that LVI was more likely in the setting of moderate-to-high tumor grade, 1-2 cm size, pancreatic head location, and high mitotic rate. Among patients with ≥2 of these 4 factors, 25% were node-positive. Conclusions: Presence of LVI was the strongest predictor of node positivity. LVI on endoscopic biopsy should prompt resection and regional LN dissection to fully stage patients with small p-NETS. Patients with other high-risk factors should also be considered for resection and regional lymphadenectomy.