The importance of microvascular invasion in patients with non-functioning pancreatic neuroendocrine neoplasm.

Background/objectives: The oncological importance of lymphatic, microvascular, and perineural invasions and their association with outcomes in patients with non-functioning pancreatic neuroendocrine neoplasm (NF-PanNEN) remains unclear. We aimed to investigate the role of these factors in the prognosis of patients with NF-PanNEN.

Methods: We retrospectively analyzed 115 patients who underwent curative resection and were pathologically and clinically diagnosed with NF-PanNEN. We evaluated the relationship between clinicopathological factors and recurrence.

Results: Thirty (26%), 38 (33%), and 11 (10%) patients had lymphatic, microvascular, and nerve invasions, respectively. Twenty-one patients (18%) experienced recurrence, with a median time to recurrence of 2.6 years (range: 0.3-8.2). The 3-, 5-, and 10-year recurrence-free survival (RFS) rates were 88.3%, 84.4%, and 79.1%, respectively. In multivariate analyses, World Health Organization Grade G2-3 (vs. G1, hazard ratio (HR): 16.2), T factor T3-4 (vs. T1-2, HR: 5.2), and the presence of microvascular invasion (vs. absence, HR: 5.6) were significant risk factors for RFS. When these risk factors were assigned as risk score of three, one, and one points depending on the HR, the 5-year recurrence rates in patients with risk score groups 0-1 and 2-5 were 98.6% and 53.3%, (P < 0.001). Moreover, only the presence of microvascular invasion significantly increased the likelihood of recurrence within 3 years.

Conclusions: The presence of microvascular invasion is an independent risk factor for recurrence in patients with NF-PanNEN. Our risk scoring system, which includes "the presence of microvascular invasion," may be useful for predicting recurrence.