The management of gastroduodenal neuroendocrine tumor (NET) has been controversial between radical surgical resection and local excision including endoscopic resection. A gastroduodenal NET grade (G), measured by their mitotic rate and Ki67 proliferation index, is important to predict prognosis. In this study, we aimed to compare the clinical outcomes of gastroduodenal NET according to grades in order to identify poor prognostic factors of gastroduodenal NETs. Fifty-four gastroduodenal NETs diagnosed between December 2008 and December 2020 in a tertiary referral hospital were retrospectively reviewed. The clinical outcomes of gastroduodenal NETs, according to tumor grades and factors associated with NET G2-3, were analyzed. A total of 52 gastroduodenal NET patients was enrolled. The mean follow-up period was 56.2 ± 40.1 months. The mean size of gastric and duodenal NET was 7.9 ± 11.0 mm and 9.8 ± 7.6 mm, respectively. During the study period, 72.7% (16/22) of gastric NETs and 83.3% (25/30) of duodenal NETS were G1. All G1 gastroduodenal NETs showed no lymph node or distant metastasis during the study periods. All G3 gastroduodenal NETs showed metastasis (one lymph node metastasis and 3 hepatic metastases). Among metastatic NETs, the smallest tumor size was a 13 mm gastric G3 NET. Factors associated with G2-3 NETs were larger tumor size, mucosal ulceration, proper muscle or deeper invasion, and lymphovascular invasion. A small-sized gastroduodenal NET confined to submucosa without surface ulceration may be suitable for endoscopic resection. After local resection of a gastroduodenal NET (G1) without lymphovascular and muscle proper invasion, follow-up examination without radical surgical resection can be recommended. G3 NETs may be treated by radical surgical resection, regardless of tumor size.
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