[Definition and histologic characterization of neuroendocrine tumors]

Neuroendocrine tumours are defined by a common phenotype, which is not supported by a common embryologic origin. This common phenotype is characterized by the expression of general neuroendocrine markers, and sometimes by cell specific hormonal products. Neuroendocrine tumours are ubiquitous, but the major localizations are the digestive tract. According to the classification of lung tumours, they are divided in low grade and high grade tumours. Since most digestive and pancreatic tumours are low grade tumours, a specific classification of neuroendocrine tumours was recently proposed. Size, degree of invasion, major secretion, and proliferation rate are the main criteria of this classification. Most neuroendocrine tumours are sporadic. A few cases occur in the context of a multiple endocrine neoplasia type 1.