This is because of the frequent multiplicity of the tumors in MEN1/ZES patients [77,78,79,80,81]; the fact that gastrinomas may be microscopic in size and not localizable by even the most sensitive imaging techniques [77,82,83,84]; gastrinomas frequently (>50%) metastasize to adjacent lymph nodes and resections are incomplete [9,43,77,81,84,85]; and 20–40% of all ZES patients present with unresectable hepatic metastases [19,20,22,86,87]. This evidence concerns the gene MEN1 and gastrin-producing neuroendocrine tumor.