<prompt> A 28-year-old man is evaluated for recurrent peptic ulcer disease, apparently refractory to pharmacologic intervention. Serum gastrin is markedly elevated. These findings are most characteristic of which of the following?Cushing syndromeGlucagonomaWhipple triadZollinger-Ellison syndrome  <response>: - Recurrent intractable peptic ulcer disease is suggestive of Zollinger-Ellison syndrome characterized by excess gastrin production, most often from a gastrinoma. - Cushing syndrome results from excess of coisol caused dt adrenal pituitary adenoma. - Glucagonoma is rare neuroendocrine tumor of pancreatic alpha cells, that can cause hyperglycemia. - Whipple triad episodic hyperinsulinemia hypoglycemia causing CNS dysfunction, reversible by glucose administration is seen with insulinoma. 