Classification of Gastric Neuroendocrine Tumors and Associations With Survival

Background and Objectives: Not all gastric neuroendocrine tumors (GNETs) may be classified into one of the three described clinicopathologic subtypes. The purpose of this study was to better characterize GNET subtypes and associated outcomes. Methods: Patients treated for GNET at our institution (1995-2021) were identified. Pathologic specimens of tumors that could not be classified as type 1, 2, or 3 were further reviewed. GNETs were categorized as proton pump inhibitor (PPI)-associated based on changes in the background gastric mucosa consistent with PPI use. Distant metastasis at presentation (DM) and disease-specific survival (DSS) were evaluated. Results: Among 246 patients, there were 164 (67%) type 1, 5 (2%) type 2, 52 (21%) type 3, and 18 (7%) PPI-associated GNETs. Seven (3%) tumors remained unclassified. DM was more frequent with type 3 GNETs (38%) than type 1 (1%), type 2 (20%), or PPI-associated tumors (11%, p < 0.001). Ten-year DSS rates were 100% for type 1, 53% (95% confidence interval [CI], 38%-75%) for type 3, and 80% (95% CI, 58%-100%) for PPI-associated tumors (p < 0.001). GNET subtype, race, and DM were independently associated with DSS. Conclusions: PPI-associated tumors may represent a distinct GNET subtype with intermediate outcomes. Other factors should also be considered in overall prognosis.