Gastroenteropancreatic endocrine/neuroendocrine tumors: Current pathological-diagnostic view

Gastroenteropancreatic endocrine or neuroendocrine tumors (NETs) encompass a broad spectrum of neoplasms characterized by a heterogeneous biological b ehavior. They differ with regard to functional state, localization,and deri vation 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 somet imes also in the setting of a familial cancer syndrome such as in type 1 mu ltiple endocrine neoplasia or von Hippel-Lindau syndrome. The complex manif estations of NETs are reflected by the varying terms and classification sys tems. However,the terms "carcinoid" and islet cell tumor" do not indicate w hether the tumors are benign, malignant, or of uncertain behavior. New clin ical, morphological, and molecular developments in the field of neuroendocr ine biology are contributing to the identification and characterization of NETs and are considered in the current World Health Organization classifica tion.