Tumor grade 2 as the independent predictor for lymph node metastasis in 10–20 mm sized rectal neuroendocrine tumor

PURPOSE: Rectal neuroendocrine tumors (NETs) <10 mm are endoscopically resected, while those ≥20 mm are treated with radical surgical resection. The choice of treatment for 10–20 mm sized rectal NETs remains controversial. This study aimed to verify factors predicting lymph node metastasis (LNM) of 10–20 mm sized rectal NET and utilize them to decide upon the treatment strategy. METHODS: Twenty-eight patients with 10–20 mm sized rectal NETs treated at Pusan National University Yangsan Hospital from January 2009 to September 2020 were divided into LNM (+) and LNM (−) groups, and their respective data were analyzed. RESULTS: Seven patients (25%) had LNM while 21 patients (75%) did not. Endorectal ultrasound findings showed tumor size was significantly larger in the LNM (+) than in the LNM (−) group (15 mm vs. 10 mm, P=0.018); however, pathologically, there was no significant difference in tumor size (13 mm vs. 11 mm, P=0.109). The mitotic count (P=0.011), Ki-67 index (P=0.008), and proportion of tumor grade 2 patients (5 cases, 71% vs. 1 case, 5%; P=0.001) were significantly higher in the LNM (+) group. In multivariate analysis, tumor grade 2 was the independent factor predicting LNM (odds ratio, 61.32; 95% confidence interval, 3.17–1,188.64; P=0.010). CONCLUSION: Tumor grade 2 was the independent factor predicting LNM in 10–20 mm sized rectal NETs. Therefore, it could be considered as the meaningful factor in determining whether radical resection is necessary.