Carcinoid syndrome is a disease consisting of a combination of symptoms, physical manifestations, and abnormal laboratory findings. Carcinoid syndrome is seen in individuals who have an underlying carcinoid tumour with spread to the liver. Carcinoid tumors are well-differentiated neuroendocrine tumours with secretory properties, releasing serotonin, along with a number of other active peptides. These tumors can arise anywhere along the primitive gut and are therefore found in the bronchial tree (airways) and along the gastrointestinal tract. The tumor cells can also migrate (metastasize) to the liver.
Carcinoid tumors most commonly occur in the small intestine and appendix, but 10% originate in the lung. Other affected areas include the rectum, colon, pancreas, stomach, ovary, thymus, kidney, prostate, breast and elsewhere. These slow-growing malignancies tend to spread to lymph nodes and the liver but can also metastasize to lung, bone, brain, and skin.
Only about 10% of the people with a carcinoid tumor will develop carcinoid syndrome. Major symptoms of this syndrome include hot, red facial flushing, diarrhea and wheezing. Carcinoid syndrome occurs when the tumor produces excessive amounts of serotonin in an individual with liver metastases. In patients who have no spread to the liver, the serotonin released by an intestinal tumor will be broken down to an inactive substance; thus, carcinoid syndrome does not occur.