GAST and Zollinger-Ellison syndrome: Lastly, gNENs can be classified into three subtypes: type 1 g-NETs which are the most frequent and develop due to hypergastrinaemia in the context of autoimmune atrophic gastritis; type 2 that are linked to increased gastric secretion, in the context of gastrin-secreting tumors, often in patients with MEN-1 and as part of a ZES; lastly, type 3 tumors are sporadic and usually poorly differentiated, mimicking malignant neoplasms of the stomach (136).