Gastric neuroendocrine tumor

Last revised by Bruno Di Muzio on 11 Dec 2022

Gastric neuroendocrine tumors (GNETs), previously known as gastric carcinoids, are rare primary neoplasms that arise from enterochromaffin-like cells of the gastric mucosa.

GNETs account for less than 2% of all gastric neoplasms and up to 10% of all gastrointestinal neuroendocrine tumors 3. Annual incidence in the United States and Europe is inferior to 0.5/100000 habitants 2 and is higher in Asia 3. Global incidence has been increasing in the last decades, possibly explained by widespread access to endoscopy 1-3.

GNETs have been subgrouped into three main clinicopathologic subtypes based on the presence of associated gastritis and elevated gastrin levels 3:

  • type 1

    • autoimmune atrophic gastritis resulting in achlorhydria, elevated stomach pH, and gastrin levels

    • tumors themselves tend to be asymptomatic, with symptoms being related to the background gastritis - e.g. dyspepsia and pernicious anemia 1,3

    • ~80% of all GNETs 1,3

  • type 2

    • existing gastrinoma leading to elevated gastrin levels and Zollinger-Ellison syndrome

    • symptoms are related to the background syndrome and not to the tumors

    • close to a third of patients have associated MEN1 syndrome 3

    • ~5% of all GNETs 1,3

  • type 3

    • sporadic

    • normal gastrinemia 1-3

    • weight loss, epigastric pain, and anemia related to tumor ulceration are common symptoms 1-3

    • ~10% of all GNETs 3

As per the 2019 revised World Health Organization (WHO) pathologic definitions of gastrointestinal tumors, these neoplasms are divided into well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs) 4.

Type 1 GNETs occur in the setting of achlorhydria and elevated stomach pH secondary to autoimmune atrophic gastritis. In this environment, gastrin secretion increases and works as a growth factor leading to enterochromaffin-like cells hyperplasia, which has potential progression to atypia 3.

GNETs are generally small, solid, and arterially hypervascular popypoid masses in the stomach 1-3. They might be occult on CT/MRI, in particular, when the stomach is collapsed.

Particularities are seen across the different clinicopathologic subtypes:

  • type 1 and type 2

    • multiple intraluminal polyps

    • usually <2cm

    • type 1 shows associated atrophic gastric mucosa, which is thin and featureless, whereas type 2 exhibits hypertrophic mucosa with diffuse gastric fold thickening 3

  • type 3

    • larger and solitary stomach mass 3

    • enhancement pattern is usually non-characteristic

    • ulceration and local invasion are common

    • associated lymphadenopathy and distant metastatic disease are not uncommon 2

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