Number, not size, of mesenteric tumor deposits affects prognosis of small intestinal well-differentiated neuroendocrine tumors.

Mesenteric tumor deposits are an adverse prognostic factor for small intestinal well-differentiated neuroendocrine tumors. Per the American Joint Committee on Cancer (AJCC) Cancer Staging Manual (eighth edition), any mesenteric tumor deposit larger than 2 cm signifies pN2 disease. This criterion has not been critically evaluated as a prognostic factor for small intestinal neuroendocrine tumors, nor have multifocality or histologic features of mesenteric tumor deposits. We evaluated 70 small intestinal neuroendocrine tumors with mesenteric tumor deposits for lesional contour, sclerosis, inflammation, calcification, entrapped blood vessels, and perineural invasion. Ki67 proliferative indices of the largest mesenteric tumor deposit from each case were calculated, and number of tumor deposits and size of the largest deposit were recorded. Associations between these factors (along with patient age, primary tumor Ki67 index, and AJCC stage) and development of liver metastases and overall survival were assessed. Median mesenteric tumor deposit size was 1.5 cm (range: 0.2-7.0 cm); median deposit number was 1 (range: 1-13). Primary and tumor deposit Ki67 indices within a given patient were discordant in 40% of cases but showed similar hazard ratios for disease-specific survival. Size of tumor deposits had no significant effect on prognosis, whether analyzed on a continuous scale or dichotomized using the recommended 2 cm cutoff. In contrast, increasing number of deposits was associated with poor prognosis, with multiple deposits conferring an 8.19-fold risk of disease-specific death compared to a single deposit (P = 0.049). Morphologic features of deposits had no prognostic impact. Size of mesenteric tumor deposits does not affect prognosis in small intestinal neuroendocrine tumor patients; instead, deposit multifocality is associated with shorter disease-specific survival and should be incorporated into future staging criteria.