A 45-year-old man presents with an upper GI bleed. An upper endoscopy reveals multiple duodenal ulcers and an enlarged stomach. Select the most likely diagnosis.

Gastrinoma, or Zollinger-Ellison syndrome, should be suspected in patients with peptic ulcer disease refractory to medical treatment, or in patients with multiple ulcers or ulcers in uncommon locations. Gastrin secretion by the tumor, most commonly found in the pancreas, results in hypersecretion of gastric acid. Common patient complaints are epigastric pain, melena, hematemesis, diarrhea, and weight loss. ZES may occur as part of the MEN-1 syndrome; this patient presents with only atypical peptic ulcer disease. The treatment of choice involves the identification and resection of the gastrinoma. Preoperative treatment may include treatment of the ulcers with omeprazole.