Neuroendocrine Tumors, Gastric

Key Features

• Gastric neuroendocrine tumors (NETs)

  • Rare

  • Account for < 1% of gastric neoplasms

  • Sporadic or secondary to chronic hypergastrinemia

• Gastric NETs secondary to chronic hypergastrinemia

  • Type 1 gastric NETs occur in association with pernicious anemia (75% of cases)

  • Type 2 gastric NETs occur with Zollinger-Ellison syndrome in multiple endocrine neoplasia type 1 (MEN 1) (5%)

  • Tend to be multicentric, < 1 cm, with low potential for metastatic spread to the liver and thus unlikely to cause the carcinoid syndrome

• Type 3 gastric NETs arise sporadically, independent of gastrin production, and account for up to 20% of all gastric NETs

Clinical Findings

• Most asymptomatic, detected incidentally during endoscopy

• May ulcerate, causing occult GI bleeding and anemia

• Most sporadic gastric carcinoids are solitary, > 2 cm in size, and have a strong propensity for hepatic or pulmonary metastases

Diagnosis

• Initial diagnostic work-up includes serum gastrin level, upper endoscopy, and endoscopic ultrasound

• Gastrin level should be obtained after the patient has stopped taking proton pump inhibitors for 1 week

• For low-grade tumors (ki-67 < 3% or < 2 mitoses/10 HPF), somatostatin receptor-based imaging (somatostatin receptor scintigraphy or gallium-68 dotatate PET/CT) should be performed

• For high-grade tumors (ki-67 > 20% or > 20 mitoses/10 HPF), FDG-PET/CT is preferred to evaluate the extent of disease

• Serum vitamin B₁₂ and intrinsic factor antibody levels should be obtained to exclude pernicious anemia

• In type 2 carcinoids associated with Zollinger-Ellison syndrome in MEN 1, chromosomal loss of 11q13 has been reported

• CT or MRI should be obtained to evaluate for metastatic disease

• Advanced, low-grade gastric NETs can be monitored with serial scans, if asymptomatic

Treatment

• Small lesions: endoscopic resection followed by periodic endoscopic surveillance or with observation

• Antrectomy reduces serum gastrin levels and may lead to regression of small tumors

• Octreotide therapy may be appropriate for patients with underlying gastrinoma and Zollinger-Ellison syndrome

• Patients with tumors > 2 cm in size should undergo endoscopic or surgical resection

• Localized sporadic NETs should be treated with radical gastrectomy and regional lymphadenectomy

• Sandostatin analogs may provide symptomatic relief for patients with functional gastric NETs

• Advanced high-grade gastric neuroendocrine carcinomas (NEC) are treated in a fashion similar to small cell lung cancers