Management of gastric and duodenal neuroendocrine tumors

Abstract

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 follow-up, 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.

Keywords: Classification; Duodenal neuroendocrine tumors; Endoscopic submucosal dissection; Endoscopic treatment; Gastric neuroendocrine tumors.

Figure 1

Gastric neuroendocrine tumor. A: Conventional endoscopic image with white light demonstrates a hemispherical reddish submucosal tumor; B: Magnifying endoscopic image with narrow band imaging demonstrates gastric pit structures present on the surface of the tumor; C: Endoscopic ultrasound (EUS, 20 MHz) demonstrates a hypoechoic intramural structure in the second layer, which corresponds to the submucosal layer of the gastric wall. EUS: Endoscopic ultrasonography.

Figure 2

Duodenal neuroendocrine tumor. A: Conventional endoscopic image with white light demonstrates a hemispherical reddish polyp with central depression; B: Magnifying endoscopic image with narrow band imaging demonstrates duodenal mucosal pit structures present on the entire surface of the tumor except the area over the central depression. Pit structures are absent over the central depression, and instead, cyan colored, cork-screw shaped, thick capillaries are seen; C: Endoscopic ultrasound (EUS, 20 MHz) demonstrates a slightly hyperechoic intramural structure in the second layer, extending to the third layer (corresponding to the duodenal muscularis propria). EUS: Endoscopic ultrasonography.

Figure 3

Management of duodenal neuroendocrine tumors. D-NETs: Duodenal neuroendocrine tumors; EUS: Endoscopic ultrasound; CT: Computed tomography; N+: Lymph node metastasis; M+: Distant metastasis; SRS: Somatostatin receptor scintigraphy; PRRT: Peptide receptor radionuclide therapy; SSA: Somatostatin analogues; CHT: Chemotherapy.