Histologically, most (62%) Amp-NETs belong to SOM-NET subtype (a histologic subtype with strong and selective preference for the major/minor ampullary regions, where it is very rarely, if ever, associated with a full-blown clinical somatostatinoma syndrome), followed by conventional NETs (29%), a fraction (11%) of which are associated with a hyperfunctioning syndrome (two gastrinomas associated with Zollinger-Ellison syndrome and one ACTH-producing NET associated with Cushing syndrome). This evidence concerns the gene POMC and gastrin-producing neuroendocrine tumor.