A gastrinoma (Zollinger-Ellison syndrome) is a gastrin-secreting neuroendocrine tumor that is most often localized to the duodenum and pancreas. Most gastrinomas occur sporadically, but some are associated with other endocrine neoplasias (e.g., pituitary adenomas, parathyroid adenomas, insulinomas). Although some gastrinomas are benign, more than half of all gastrinomas are malignant. Gastrinomas release high levels of gastrin, which then increases the production of gastric acid. Patients typically present with recurrent, therapy-resistant peptic ulcer disease and diarrhea. Patients with gastrinomas have low gastric pH and elevated serum gastrin. Furthermore, serum gastrin levels increase with the administration of secretin (positive secretin stimulation test). Surgical resection of the tumor is indicated in patients with localized disease. Proton pump inhibitors (PPIs) and octreotide may be used to control acid secretion.
- Gastrinomas are neuroendocrine tumors of the GI tract that secrete gastrin.
- Hypergastrinemia → stimulation of parietal cells → gastric acid hypersecretion, which leads to:
- ∼ 60% of gastrinomas are malignant (but slow-growing) 
- Best initial test: esophagogastroduodenoscopy
- ↑ Serum gastrin (in a fasting serum sample)
Secretin stimulation test (if fasting serum gastrin test is inconclusive)
- In healthy individuals, secretin inhibits gastrin secretion.
- In patients with gastrinomas, secretin causes a paradoxical and dramatic increase in the levels of gastrin within a few minutes of administering secretin.
- A two-fold increase in gastrin above the basal level is indicative of a gastrinoma.
- No increase or only a very slight increase is observed in cases of secondary hypergastrinemia.
Imaging: only after diagnosis is confirmed to localize the tumor
- CT/MRI scan, somatostatin receptor scintigraphy (octreotide scan) and/or endoscopic ultrasonography
- Tumor location 
- Reduce acid production
- Nonmetastatic disease: surgical resection of the gastrinoma
- Metastatic disease: chemotherapy