Gastrointestinal carcinoids--aspects of diagnosis and classification.

Gastrointestinal carcinoids are a heterogeneous group of hormone-producing tumours originating from the diffuse neuroendocrine system of the gastrointestinal mucosa. Recent studies have shown that carcinoid tumours share many of the morphological, biochemical and functional properties of the neuroendocrine cells from which they are derived. Identification of these properties, e.g. specific hormone production, contents of secretory granules or specific proteins of the secretory granules/ vesicles, forms the basis for the diagnosis of carcinoid tumours. Classification of gastrointestinal carcinoids is based on the clinical settings under which the tumours develop, tumour site, as well as the morphological and biochemical characteristics of the tumour. Although generally considered a low grade malignancy, carcinoid tumours show a highly variable clinical course from benign tumours discovered incidentally to highly malignant tumours presenting with disseminated spread and disabling hormonal symptoms. Precise knowledge of tumour location, size and stage, as well as growth pattern and hormonal syndromes, is necessary to predict the behaviour of the tumour and optimise treatment.