Pathological features associated with lymph node disease in patients with appendiceal neuroendocrine tumors.

238 Background: Appendiceal neuroendocrine tumors (ANETs) are well known for their benign and slow progression; nonetheless, the presence of lymph node metastasis has been described in up to 50% of all cases. The risk of metastasis is mainly associated with tumor size, and the role of other pathological features remains unclear. Hence, this study was designed to assess the pathologic features of ANETs associated with an increased risk of lymph node metastasis. Methods: Patients ≥18yrs of age with ANETs were identified in the National Cancer Database (NCDB) from 2004 to 2017. Groups were defined based on lymph node status as N(-) (all examined nodes were negative) and N(+) (one or more examined nodes were positive). Multivariable models using demographics and oncological features were used to identify factors independently associated with nodal metastasis (N+). Marginal effects, specifically for tumors <2 cm were also calculated. Results: A total of 2,465 cases were identified and included for data analysis. Among these, 23% had lymph node metastases, including 33 of 979 tumors <1 cm (3.4%), and 145 of 696 tumors ≥1 cm but ≤2 cm (20.8%). Tumor size, depth of tumor invasion, and presence of lymphovascular invasion (LVI) were identified as independent predictors of lymph node metastasis (p <0.001). When evaluating marginal effects, both the depth of tumor invasion and the presence of LVI were associated with increased risk of node metastasis in small tumors (<2 cm), comparable to the mere risk of node metastasis in big tumors (≥2cm). In addition, for small ANETs (<2cm), the true positive rates (TPR) of node metastasis vary according to the number of assessed lymph nodes, differing significantly between patients with at least 12 evaluated lymph nodes vs. those with less than 12 (TPR 4.7% vs. 1.6% for <1 cm [p =0.02], and 40.1% vs. 25.7% in ≤2 cm ANETs, [p <0.001]). Conclusions: In ANETs, the presence of high-risk pathological features, including LVI and tumor depth, increases the risk of node metastasis in addition to tumor size, and should be considered when selecting the optimum management and follow-up in these patients. [Table: see text]