In addition, the distribution of the tumor grades in patients with gastrinomas with MEN1/ZES differed from those with sporadic ZES in having more patients with lower grades (G1: 83% vs. 39%; G2 (11% vs. 54%) G3: (5.6% vs. 6.1%) [337]. This evidence concerns the gene MEN1 and gastrin-producing neuroendocrine tumor.