Carcinoid tumors and carcinoid syndrome

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Carcinoid tumors are noncancerous (benign) or cancerous (malignant) growths that sometimes produce excessive amounts of hormone-like substances (such as serotonin ), resulting in the carcinoid syndrome. Carcinoid syndrome is a group of specific symptoms that occur as a result of these hormones.

People with carcinoid tumors may have cramping pain and changes in bowel movements.
People with carcinoid syndrome usually have flushing and sometimes diarrhea.
Doctors measure the amount of a serotonin byproduct in a person’s urine.
Imaging tests are needed to determine tumor location.
Sometimes tumors are removed surgically.
People may need to take drugs to control symptoms.

Carcinoid tumors (sometimes called neuroendocrine tumors) usually originate in hormone-producing cells that line the small intestine or other parts of the digestive tract. They can also occur in the pancreas, lungs (bronchial carcinoid), or rarely the testes or ovaries.
Carcinoid tumors can produce an excess of hormone-like substances, such as serotonin , bradykinin, histamine, and prostaglandins. Excess levels of these substances can sometimes result in a diverse set of symptoms called carcinoid syndrome. Carcinoid tumors use the amino acid tryptophan to produce the excess serotonin . Because tryptophan is normally used by the body to make niacin (vitamin B3), people may rarely develop a niacin deficiency, which can cause the disease pellagra.
When carcinoid tumors occur in the digestive tract or pancreas, the substances they produce are released into a blood vessel that flows directly to the liver (portal vein), where enzymes destroy them. Therefore, carcinoid tumors that originate in the digestive tract generally do not cause symptoms of carcinoid syndrome unless the tumors have spread to the liver.
If the tumors have spread to the liver, the liver is unable to process the substances before they begin circulating throughout the body. Depending on which substances are being released by the tumors, the person will have the various symptoms of carcinoid syndrome. Carcinoid tumors of the lungs, testes, and ovaries also cause symptoms because the substances they produce bypass the liver and circulate widely in the bloodstream.