Gastroenteropancreatic neuroendocrine neoplasms Diagnosis and classification

Neuroendocrine neoplasms of the gastroenteropancreatic system are subdivided based on morphological criteria into well-differentiated neuroendocrine neoplasms (neuroendocrine tumors) and poorly differentiated neuroendocrine neoplasms (neuroendocrine carcinomas). Neuroendocrine neoplasms are of epithelial origin and express neuroendocrine markers. Neuroendocrine tumors are characterized by an organoid growth pattern. The grading into G1, G2, or G3 tumors is based on the Ki67 proliferative index. Gastroenteropancreatic neuroendocrine tumors show site-specific features with differences in morphology, hormonal expression, biological behavior, metastatic potential, and prognosis. The European Neuroendocrine Tumor Society (ENETS) has published guidelines for histopathologic diagnostics and standard of care in neuroendocrine tumors.