[Gastroenteropancreatic neuroendocrine/endocrine tumors. Current pathologic-diagnostic view]

Gastroenteropancreatic endocrine or neuroendocrine tumors (NETs) encompass a broad spectrum of neoplasms characterized by a heterogeneous biological behavior. They differ with regard to functional state, localization, and derivation from various segments of the primitive embryonal gut, growth pattern, degree of differentiation, expression of different neuroendocrine marker molecules, and prognosis. They occur generally as sporadic tumors but sometimes also in the setting of a familial cancer syndrome such as in type 1 multiple endocrine neoplasia or von Hippel-Lindau syndrome. The complex manifestations of NETs are reflected by the varying terms and classification systems. However, the terms "carcinoid" and islet cell tumor" do not indicate whether the tumors are benign, malignant, or of uncertain behavior. New clinical, morphological, and molecular developments in the field of neuroendocrine biology are contributing to the identification and characterization of NETs and are considered in the current World Health Organization classification.