In MEN1/ZES patients the gastrinomas are similar to those in sporadic ZES patients in that they are primarily duodenal in location and frequently associated with lymph node metastases; however, they differ in MEN1/ZES from sporadic ZES in that the MEN1 duodenal gastrinomas are almost variably multicentric, smaller, and multiple [334,335,336,337,338], as well as the fact they differ in biological behavior in that the rate of liver metastases is significantly higher in sporadic cases than in MEN1/ZES patients [337]. This evidence concerns the gene MEN1 and gastrin-producing neuroendocrine tumor.