MEN1 and Zollinger-Ellison syndrome: Therefore, the combination of early onset of ZES in MEN1 patients, combined with lifelong chronic hypergastrinemia and mutations in the MEN1 gene predisposing them to the development of endocrine tumors, these patients not only very frequently develop advanced ECL cell changes, but also gastric carcinoids, which are more aggressive than type 1 sporadic gastric carcinoids in CAG/PA or other hypergastrinemia states [42,61,115,116,121].