Evaluation of the Significance of Lymphatic, Microvascular and Perineural Invasion in Patients With Pancreatic Neuroendocrine Neoplasms.

Background: Some prognostic factors for pancreatic neuroendocrine neoplasms (PanNENs) have been reported; however, the significance of lymphatic, microvascular, and perineural invasion remains unclear. We aimed to clarify the role of these factors in PanNEN recurrence. Patients and Methods: We analyzed 138 patients who underwent curative pancreatectomy and were pathologically diagnosed with PanNEN. We evaluated the association between clinicopathological factors and the recurrence of PanNENs. Results: The numbers of patients with lymphatic, microvascular, and perineural invasion were 34 (25%), 43 (31%) and 17 (12%), respectively. Twenty-four patients (17%) had recurrences, and the 3, 5, and 10-year recurrence-free survival (RFS) rates were 88%, 84%, and 76%, respectively. The recurrence sites (with duplication) were mainly the liver (twenty-two patients), followed by the lymph nodes (seven patients), and bone (two patients). In multivariate analyses, grade 2-3 and the presence of microvascular invasion were significant risk factors for RFS (hazard ratio=7.5 and 7.9, respectively). When examining outcomes according to these factors, the 5-year RFS rates of patients with risk scores of 0, 1, and 2 were 100%, 91%, and 32%, respectively (p<0.001). Even in patients with grade 1 (n=97) or limited resection (enucleation, splenic-preserving distal pancreatectomy, central pancreatectomy, and duodenum-preserving pancreatic head resection, n=62), the presence of microvascular invasion was a significant risk factor for RFS (hazard ratio=13.4 and 18.0, respectively). Conclusion: The presence of microvascular invasion is an independent risk factor for recurrence in patients with PanNEN.