Review article: current status of gastrointestinal carcinoids

Carcinoid tumours are enigmatic, slow growing malignancies which occur most frequently (74%) in the gastrointestinal tract. In recent years, it has become apparent that the term 'carcinoid' represents a wide spectrum of different neoplasms originating from a variety of different neuroendocrine cell types. Carcinoid lesions are usually identified histologically by their affinity for silver salts, by general neuroendocrine markers, or more specifically by immunocytochemistry using antibodies against their specific cellular products. Within the gut, the most frequent sites are the small bowel (29%), the appendix (19%) and rectum (13%). Clinical manifestations are often vague or absent. Nevertheless, in approximately 10% of patients the tumours secrete bioactive mediators which may engender various elements of characteristic carcinoid syndrome. In many instances the neoplasms are detected incidentally at the time of surgery for other gastrointestinal disorders. The tendency for metastatic spread correlates with tumour size, and is substantially higher in lesions larger than 2.0 cm. An association with noncarcinoid neoplasms is ascribed in 8-17% of lesions. Treatment consists of radical surgical excision of the tumour, although gastric (type I and II) and rectal carcinoids may be managed with local excision. Overall 5-year survival is excellent for carcinoids of the appendix (86%) and rectum (72%), whereas small intestinal (55%), gastric (49%) and colonic carcinoids (42%) exhibit a far worse prognosis.