Zollinger-Ellison syndrome (ZES) is a condition in which one or more tumors called gastrinomas form in the pancreas or upper small intestine and produce excessive amounts of the hormone gastrin. Gastrin signals the stomach to make acid, so when levels climb far above normal, the stomach churns out so much acid that it damages its own lining and the intestines. The result is severe, recurring peptic ulcers and often persistent diarrhea that doesn’t respond to typical treatments.
ZES is rare, but it’s important to recognize because it behaves very differently from ordinary ulcers and acid reflux. The excess acid drives complications that standard doses of antacid medications can’t control, and the underlying tumor is malignant in a significant number of cases.
How Gastrinomas Cause the Problem
Gastrin is a normal hormone. After you eat, cells in the stomach lining release it to ramp up acid production for digestion. Once the food is broken down, acid levels rise, and gastrin secretion shuts off. Gastrinomas bypass that feedback loop entirely. These small neuroendocrine tumors secrete gastrin continuously, regardless of how much acid is already present. The stomach’s acid-producing cells respond by multiplying and working overtime.
The vast majority of gastrinomas sit inside a small anatomical region sometimes called the “gastrinoma triangle,” bounded roughly by the junction of the bile ducts, the second and third portions of the duodenum, and the junction of the pancreatic head and neck. Some tumors are tiny, only a few millimeters, which makes them notoriously difficult to find on imaging.
Symptoms to Recognize
The most common symptoms overlap with ordinary peptic ulcer disease and gastroesophageal reflux (GERD), which is part of the reason ZES often goes undiagnosed for years. Typical complaints include a burning or dull pain between the navel and the middle of the chest, heartburn, nausea, and vomiting. Some people experience bleeding in the digestive tract, unintentional weight loss, or loss of appetite.
Diarrhea is a hallmark of ZES and sometimes the only symptom. The massive volume of acid flooding into the small intestine overwhelms its ability to absorb water and nutrients. If you have chronic diarrhea alongside ulcer symptoms, especially ulcers that keep coming back despite treatment, that combination is a red flag.
Doctors typically suspect ZES when a patient has peptic ulcers that are unusually severe, recur repeatedly, or resist standard therapy, particularly when there’s no evidence of H. pylori infection and no history of regular anti-inflammatory drug use.
How ZES Is Diagnosed
The first step is a blood test measuring fasting serum gastrin. A level more than ten times the upper limit of normal (generally above 1,000 pg/mL) in a patient whose stomach pH is highly acidic (pH of 2 or lower) is considered diagnostic on its own. Many patients, however, fall below that threshold, which is where a provocation test comes in.
In the secretin stimulation test, you receive an injection of the hormone secretin. In a healthy person, secretin has little effect on gastrin. In someone with a gastrinoma, gastrin levels spike dramatically. An absolute rise of 120 pg/mL or more after injection is the most reliable cutoff, carrying about 94% sensitivity with virtually no false positives.
Once the bloodwork confirms ZES, the next challenge is finding the tumor. Endoscopic ultrasound is extremely sensitive (around 93%) for detecting small pancreatic neuroendocrine tumors and outperforms standard CT or MRI. The current preferred imaging method for pinpointing gastrinomas is a specialized PET scan using a radioactive tracer that binds to receptors on the tumor surface, which can reveal tumors too small for conventional scans to catch.
The Link to MEN1
About 75 to 80 percent of ZES cases are sporadic, meaning they arise on their own with no known genetic cause. The remaining 20 to 25 percent occur as part of a hereditary condition called Multiple Endocrine Neoplasia type 1 (MEN1), which causes tumors in several hormone-producing glands, including the parathyroid, pituitary, and pancreas.
The distinction matters because MEN1-associated ZES behaves differently. Patients with MEN1 tend to develop multiple gastrinomas rather than a single tumor, making complete surgical removal far more difficult. They also face a significantly higher risk of developing gastric carcinoid tumors: estimates range from 23 to 70 percent in MEN1/ZES patients, compared with less than 1 percent in sporadic ZES. That difference is roughly 70-fold. Screening for MEN1 through genetic testing and measuring calcium and parathyroid hormone levels is a standard part of the workup once ZES is confirmed.
Controlling Acid With Medication
Proton pump inhibitors (PPIs) are the cornerstone of medical treatment. These are the same class of drugs used for ordinary acid reflux, but ZES patients need much higher doses. A typical starting regimen is two to four times the standard reflux dose, taken twice daily rather than once. Doctors then adjust based on measured acid output, with some patients requiring even higher amounts to bring acid secretion under control.
PPIs are effective at healing ulcers and relieving symptoms in the vast majority of ZES patients, and most people tolerate them well over the long term. However, medication only manages the acid. It does nothing about the gastrinoma itself, which is why surgery plays a central role.
Surgery and Long-Term Outlook
Surgical removal of the gastrinoma is the only chance for a cure. In a large study from the National Institutes of Health, 94 percent of patients who underwent surgery had a tumor successfully removed, and 51 percent were cured immediately. At long-term follow-up, 41 percent remained disease-free. For sporadic ZES specifically, about 34 percent of patients stayed free of disease at 10 years.
The survival advantage of surgery is striking. Fifteen-year disease-related survival was 98 percent for patients who had surgery, compared with 74 percent for those who did not. Patients who skipped surgery were also far more likely to develop liver metastases (29 percent versus 5 percent), which is the main driver of poor outcomes in ZES.
The overall 10-year survival rate across all ZES patients is about 94 percent, reflecting the fact that gastrinomas, while malignant, often grow slowly. Prognosis depends heavily on whether the tumor has spread. Localized disease that can be surgically removed carries an excellent outlook. Metastatic disease to the liver, while more serious, can still be managed with a combination of targeted therapies, though cure becomes unlikely at that stage.
For patients with MEN1, the picture is more complicated. Because multiple tumors are the norm, recurrence after surgery is nearly universal. Almost all MEN1/ZES patients relapse within 10 years, compared with about two-thirds of sporadic cases. This means lifelong monitoring and ongoing acid-suppression therapy are essential regardless of surgical outcome.
Complications Beyond Ulcers
Left untreated, the relentless acid production in ZES can cause damage well beyond stomach ulcers. Severe esophageal disease, including narrowing of the esophagus (stricture) and Barrett’s esophagus, a precancerous change in the esophageal lining, has been documented, particularly in MEN1/ZES patients. Chronic diarrhea can lead to malnutrition and significant weight loss. Bleeding from ulcers may cause anemia or, in acute cases, require emergency intervention.
The gastrinoma itself carries cancer risk. These tumors are neuroendocrine in origin and can metastasize, most commonly to the liver. The likelihood of metastasis increases with tumor size and delay in diagnosis, which is one of the strongest arguments for pursuing surgery early when the tumor is still localized.