Differences in Endoscopic Features of Gastric Neuroendocrine Tumor and Neuroendocrine Carcinoma From a Clinicopathological Perspective.

Gastric neuroendocrine neoplasms are a rare type of stomach cancer, classified into well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs). Gastric NETs (G-NETs) originate from endocrine progenitor cells in the basal layer of the mucosa, primarily in the setting of chronic atrophic gastritis, such as autoimmune gastritis. They generally exhibit low malignancy and a favorable prognosis. By contrast, gastric NECs (G-NECs), a rare subtype of gastric cancers, arise from endocrine precursor cell clones that dedifferentiate in the deep portion of pre-existing differentiated-type adenocarcinomas. G-NECs are characterized by rapid growth, frequent lymphovascular invasion, high metastatic potential, and aggressive biological behavior. Most G-NEC cases are therefore diagnosed at advanced stages, often with lymph node or distant metastases, leading to a poorer prognosis than gastric adenocarcinomas. Furthermore, endoscopic diagnosis of G-NECs remains challenging because of the low sensitivity of biopsy-based techniques. While it is well established that G-NETs and G-NECs have distinct clinicopathological characteristics, information on their endoscopic features, particularly those observed with magnifying narrow-band imaging, remains limited. This review aims to summarize the characteristic endoscopic findings of G-NETs and G-NECs in relation to their clinicopathological findings.