Epidemiology

Etiology

Gastrinomas are assumed to arise from endocrine cells of the gut (mostly the duodenum) or the pancreas.
Most gastrinomas occur sporadically (∼ 75% of cases).
Some gastrinomas occur in association with multiple endocrine neoplasia type 1 (MEN 1) (∼ 25% of cases).

Gastrinomas are neuroendocrine tumors of the GI tract that secrete gastrin.
Hypergastrinemia → stimulation of parietal cells → gastric acid hypersecretion, which leads to:
- Peptic ulcer disease
- Inactivation of pancreatic enzymes → diarrhea, steatorrhea → malabsorption
  - The high volume of gastric acid that is produced decreases intestinal pH. Pancreatic lipases, which require an alkaline environment to function, are inactivated and can no longer emulsify fats. Moreover, gastrin acts directly on the intestine and prevents sodium and water reabsorption, resulting in secretory diarrhea.

Most patients manifest with recurrent, therapy-resistant peptic ulcer disease.

Fasting serum gastrin (FSG) and gastric pH (initial studies)
Secretin stimulation test
- Mechanism
  - In healthy individuals, an infusion of secretin inhibits gastrin secretion.
  - In individuals with gastrinoma, secretin infusion causes a dramatic increase in gastrin secretion.
    - Gastrinoma cells have altered receptor signaling that make them respond aberrantly to secretin stimulation.
- Findings
  - ↑ Serum gastrin by > 120 pg/mL over baseline FSG confirms gastrinoma
Esophagogastroduodenoscopy (EGD)
- Single duodenal ulcers (most common) or multiple ulcers in atypical locations (e.g., distal duodenum, jejunum)
- Thick gastric folds