Management of gastric and duodenal neuroendocrine tumors

Gastrointestinal neuroendocrine tumors(GI-NETs) are rare neoplasms, like all NETs. However, the incidence of GI-NETS has been increasing in recent years. Gastric NETs(G-NETs) and duodenal NETs(D-NETs) are the common types of upper GI-NETs based on tumor location. G-NETs are classified into three distinct subgroups: type?Ⅰ, Ⅱ, and Ⅲ. Type?Ⅰ?G-NETs, which are the most common subtype(70%-80% of all G-NETs), are associated with chronic atrophic gastritis, including autoimmune gastritis and Helicobacter pylori associated atrophic gastritis. Type Ⅱ G-NETs(5%-6%) are associated with multiple endocrine neoplasia type 1 and Zollinger-Ellison syndrome(MEN1-ZES). Both type?Ⅰ?and Ⅱ G-NETs are related to hypergastrinemia, are small in size, occur in multiple numbers, and are generally benign. In contrast, type Ⅲ G-NETs(10%-15%) are not associated with hypergastrinemia, are large-sized single tumors, and are usually malignant. Therefore, surgical resection and chemotherapy are generally necessary for type Ⅲ G-NETs, while endoscopic resection and followup, which are acceptable for the treatment of most type?Ⅰ?and Ⅱ G-NETs, are only acceptable for small and well differentiated type Ⅲ G-NETs. D-NETs include gastrinomas(50%-60%), somatostatin-producing tumors(15%), nonfunctional serotonin-containing tumors(20%), poorly differentiated neuroendocrine carcinomas(< 3%), and gangliocytic paragangliomas(< 2%). Most D-NETs are located in the first or second part of the duodenum, with 20% occurring in the periampullary region. Therapy for D-NETs is based on tumor size, location, histological grade, stage, and tumor type. While endoscopic resection may be considered for small nonfunctional D-NETs(G1) located in the higher papilla region, surgical resection is necessary for most other D-NETs. However, there is no consensus regarding the ideal treatment of D-NETs.