ZOLLINGER-ELLISON SYNDROME - A tumor (gastrinoma) of the pancreatic islet cells that results in an over production of gastric acid, leading to fulminant ulceration of the esophagus, stomach, duodenum, and jejunum. Gastrinomas may also occur in the stomach, duodenum, spleen, and regional lymph nodes. Treatment includes the use of H2 antagonists (e.g. cimetidine, ranitidine). Surgical excision of the tumor is curative in approximately 25% of patients.