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Carcinoid syndrome describes a combination of symptoms that result from hormones or hormone-like substances, (e.g., serotonin, gastrin, ACTH) that are produced by some carcinoid tumors.

Normally, the body uses the amino acid tryptophan to produce niacin (a vitamin that belongs to the B complex family of vitamins) but in carcinoid syndrome, the tryptophan produces serotonin instead of niacin leading to excess amounts of serotonin circulating in the blood and a deficiency of niacin. Carcinoid tumors of the GI tract release their hormone-like substances into the portal vein which flows into the liver. The liver usually breaks these substances down preventing the initial presentation of symptoms. However, if metastases have reached the liver, it no longer can efficiently destroy the excess amounts of serotonin. This results in elevated levels of serotonin circulating freely in the blood and the appearance of related symptoms. Hence, carcinoid syndrome related to GI tumors usually presents later and indicates liver involvement.

The presence of these hormone-like substances in the bloodstream causes symptoms of carcinoid syndrome that include:

• Flushing
• Diarrhea
• Abdominal pain
• Wheezing
• Carcinoid heart disease
• Carcinoid crisis

Flushing

Flushing is redness and a feeling of warmth in the face and neck which may last from a few moments to several hours or may appear for a few moments several times a day. Flushing is present in approximately 90% of patients who experience carcinoid syndrome and is the most common symptom. It has been noted that flushing related to midgut carcinoid tumors is characterized by pink or red flushing that begins in the face and radiates to the extremities or the trunk. Flushing related to foregut tumors tends to be darker and is usually restricted to upper limbs. Flushing can be brought on by:

• Stress
• Drinking wine or alcoholic beverages
• Hot beverages
• Foods (e.g., blue cheese, walnuts, bananas, chocolate)

Diarrhea

Diarrhea occurs in approximately 70% of patients with carcinoid syndrome. It is thought that diarrhea associated with carcinoid syndrome is due to serotonin production by the tumor and drugs that block serotonin (e.g., ondansetron; Zofran) can help to better control diarrhea.

Abdominal Pain

Abdominal pain is a relatively common symptom of carcinoid syndrome and can occur as a result of the tumor spreading to other organs/tissues of the body or it may occur if the tumor causes intestinal obstruction.

Wheezing

Only about 10% of patients with carcinoid syndrome experience wheezing which is due to bronchospasm (contraction of the muscles in the walls of the bronchi and bronchioles leading to constriction of the airway).

Carcinoid Heart Disease

Carcinoid heart disease develops in up to 60% of individuals with carcinoid syndrome and is related to the effect on the vascular system exerted by the hormone-like substances such as serotonin produced by the tumor. Research indicates that serotonin is related to the progression of carcinoid heart disease and that the risk of progression is higher in people who undergo treatment with chemotherapy. The most common site of carcinoid heart disease usually involves the tricuspid valve located on the right side of the heart between the right atrium and the right ventricle.