Gastric neuroendocrine tumor

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

Epidemiology

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.

Clinical presentation

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

Pathology

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.

Radiographic features

GNETs are generally small, solid, and arterially hypervascular polypoid 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