GAST and Zollinger-Ellison syndrome: Zollinger–Ellison syndrome (ZES), which is due to ectopic secretion of gastrin from a neuroendocrine tumor (usually in the pancreas/duodenum) resulting in severe, recalcitrant peptic ulcer disease/gastro-esophageal reflux disease (GERD) [20,21,22] has been proposed to be a good model to study the lifelong effects of chronic hypergastrinemia in man [19,21,23,24,25,26,27].