[Neuroendocrine system and its tumors].

The original classification of neuroendocrine tumours proposed by Pearse was based on a common embryologic origin in the neuroectoderm. The term, carcinoid, literally means carcinoma-like, was coined in 1907 to describe the histologic similarity of these tumors to carcinomas on the one hand and their generally indolent biologic behaviour on the other hand. Neuroendocrine tumours represent a group with complex biological, histological, ultrastructural and immunocytochemical properties. This concept was replaced by another classification based on results of modern techniques (electron microscopy, immunocytochemistry, molecular and DNA analyses). This permits a more reliable classification of tumours, that can be used to determine their biological behaviour and prognosis.