Carcinoid Syndrome	

The carcinoid syndrome occurs with around ten per cent of carcinoid tumours, usually in association with midgut tumours, and almost invariably in the presence of hepatic metastases. It results from the secretion of 5-hydroxytryptamine (5HT: serotonin) and a variety of other vasoactive substances such as histamine, bradykinins, prostaglandins and substance P. 
The cardinal features of the syndrome are diarrhoea and flushing. The diarrhoea is secretory and may be profuse, with passage of several litres per day, and there are occasionally associated electrolyte disturbances. It may also be associated with cramping abdominal pain.