Zollinger-Ellison syndrome refers to gastric gland hyperplasia secondary to excessive gastrin secretion by a tumor (gastrinoma), usually found in the pancreas. The excess gastrin increases the thickness of the gastric mucosa and increases the acid production by the stom ach. This results in the formation of recurrent peptic ulcers, especially within the duodenum and jejunum. As a result, the classic clinical triad associated with the Zollinger-Ellison syndrome is the combination of increased acid production by the stomach, peptic ulcers of the duodenum and jejunum, and an islet-cell tumor of the pancreas. Ref:- Harshmohan textbook of Pathology