Neuroendocrine neoplasms of the stomach. Update on diagnostic criteria, classification, and prognostic markers.

Gastric neuroendocrine neoplasms (gNENs) encompass all the spectrum of NENs including neuroendocrine carcinomas (gNECs), mixed neuroendocrine/non-neuroendocrine neoplasms (gMiNENs) and neuroendocrine tumors (gNETs). Differently from other digestive sites, gNETs are subclassified according to the clinicopathologic setting in which they arise, with important prognostic implications. Since gastric endoscopic biopsies represent a high-volume daily activity in both referral and community hospitals, pathologists should be increasingly aware of this disease. This will allow to correctly identify the different entities and, when present, their precursor lesions, giving useful information to clinicians for the best patient management. This review paper aims to provide morphologic, immunophenotypic, and, when necessary, molecular criteria for the correct diagnosis and subtyping of gNENs. In addition, a simplified prognostic classification schema of enterochromaffin-like (ECL)-cell NETs is proposed, based on gastrin serum levels and the status of gastric acid secretion.