Zollinger-Ellison syndrome (ZES) is a condition in which small tumors called gastrinomas form in the pancreas or upper small intestine and pump out massive amounts of the hormone gastrin. That flood of gastrin drives the stomach to produce far more acid than normal, leading to severe ulcers, chronic diarrhea, and abdominal pain. It’s rare, but understanding how it works helps explain why ordinary ulcer treatments often fail in people who have it.
How Gastrinomas Cause Excess Acid
Normally, your body releases a small burst of gastrin after you eat. Gastrin is the signal that tells acid-producing cells in your stomach lining to get to work. Once digestion is underway, gastrin levels drop and acid production slows down. In ZES, gastrinomas short-circuit that feedback loop. They release gastrin continuously and in enormous quantities, so your stomach keeps churning out acid around the clock, regardless of whether you’ve eaten.
That relentless acid does two things. First, it erodes the lining of the stomach and the first section of the small intestine (the duodenum), creating ulcers that are often multiple and unusually stubborn. Second, the acid floods into the small intestine in volumes too large for the body’s normal buffering systems to neutralize. The resulting acidic environment damages the intestinal lining, interferes with digestive enzymes that break down fat, and leads to chronic diarrhea, often with greasy, foul-smelling stools from unabsorbed fat.
Where Gastrinomas Grow
Most gastrinomas develop in a small anatomical zone sometimes called the “gastrinoma triangle.” This area sits between the junction of certain bile ducts above, the second and third portions of the duodenum below, and the neck and body of the pancreas on the inner side. Roughly 80% of gastrinomas are found within this triangle, which is why imaging and surgical exploration focus there.
Gastrinomas can be benign or malignant. About 60 to 90 percent are cancerous, and some will have already spread to the liver or nearby lymph nodes by the time they’re diagnosed. In roughly 25% of cases, ZES occurs as part of a genetic condition called multiple endocrine neoplasia type 1 (MEN1), which causes tumors in several hormone-producing glands at once. If you’re diagnosed with ZES, doctors typically test for MEN1 because it changes both treatment and long-term monitoring.
Common Symptoms
ZES symptoms overlap heavily with ordinary peptic ulcers, which is one reason diagnosis is often delayed. The most common signs include:
- Burning abdominal pain in the upper abdomen, similar to a standard ulcer but often more persistent and less responsive to typical antacids
- Chronic diarrhea, present in up to half of patients and sometimes the only symptom
- Heartburn and acid reflux that doesn’t fully resolve with standard acid-reducing medication
- Nausea, vomiting, or unintended weight loss from poor nutrient absorption
The red flag that separates ZES from garden-variety ulcers is recurrence. If ulcers keep coming back despite treatment, appear in unusual locations (like the lower duodenum or jejunum), or show up alongside unexplained diarrhea, ZES should be on the radar.
How ZES Is Diagnosed
Diagnosis starts with a blood test measuring fasting gastrin levels. In ZES, these levels are dramatically elevated, often many times higher than normal. However, other conditions (including long-term use of acid-suppressing medications) can also raise gastrin, so a high reading alone isn’t enough.
When results are ambiguous, a secretin stimulation test can confirm the diagnosis. Secretin is a hormone that normally has little effect on gastrin. In this test, secretin is injected into a vein and gastrin levels are measured over the next 15 minutes. In people with ZES, gastrin spikes sharply, typically rising by more than 200 pg/mL. That paradoxical jump is highly specific to gastrinomas and essentially confirms the diagnosis.
Once ZES is confirmed biochemically, imaging is needed to locate the tumor. Specialized PET/CT scans using a radioactive tracer that binds to receptors on neuroendocrine tumor cells have become the preferred approach, with sensitivity around 81% and specificity around 90% for detecting these tumors. Endoscopic ultrasound, CT, and MRI are also used, often in combination, because gastrinomas can be small and difficult to spot.
Treatment and Acid Control
Treatment has two goals: control the acid and deal with the tumor.
Acid control comes first and is often dramatically effective. Proton pump inhibitors (PPIs), the same class of drugs used for ordinary heartburn, are the cornerstone of medical management. The difference is dosage. While a typical reflux patient might take one standard dose per day, ZES patients often need two to four times that amount, sometimes split across multiple daily doses. Fortunately, high-dose PPIs are well tolerated and can keep acid output in a safe range for years.
Surgical removal of the gastrinoma is the only potential cure. When the tumor is localized and hasn’t spread, surgery can be curative in a significant number of cases. Surgeons explore the gastrinoma triangle carefully, sometimes finding tumors as small as a few millimeters embedded in the duodenal wall or pancreas. For patients with MEN1, the surgical approach is more complex because multiple tumors are common.
When gastrinomas have already spread to the liver, surgery may still be considered to reduce tumor burden, but a cure is less likely. In those cases, additional treatments targeting the tumor’s growth, including certain injectable medications that block hormone release and other therapies aimed at slowing tumor progression, become part of the plan.
Long-Term Outlook
Prognosis depends almost entirely on whether the tumor has spread. A landmark study published in the Journal of Clinical Oncology found that patients with no liver metastases had a 10-year survival rate of 96%. For those whose gastrinomas had already reached the liver at the time of diagnosis, that number dropped to 26%.
This stark difference underscores why early diagnosis matters. Many patients live for decades with well-controlled ZES, taking daily acid-suppressing medication and undergoing periodic imaging to monitor for tumor growth or recurrence. The acid-related symptoms, once the most dangerous aspect of the disease, are now highly manageable with modern medications. The primary long-term concern is the tumor itself, particularly whether it behaves aggressively or remains slow-growing, as many neuroendocrine tumors do.