For MEN1 gastrinomas and insulinoma, the Selective Arterial Secretagogue Injection (SASI) test, and the selective intra-arterial calcium stimulation test with hepatic venous sampling for the dosage of gastrin and insulin/C-peptide, represent a valuable tool in regionalizing the area of gastrin and insulin secretion respectively, even when other diagnostic techniques do not visualize any mass, as frequently happens in duodenal gastrinoma [20,32]. This evidence concerns the gene INS and gastrin-producing neuroendocrine tumor.