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.
Carcinoid tumors usually originate in hormone-producing cells that line the small intestine or other cells of the digestive tract. They can also occur in the pancreas, testes, ovaries, or lungs. 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 to make niacin (vitamin B3), people may develop a niacin deficiency, causing the disease pellagra (see Vitamins: Niacin Deficiency).
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 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.
Most people with carcinoid tumors have symptoms similar to those of other intestinal tumors, mainly cramping pain and changes in bowel movements as a result of obstruction.
Fewer than 10% of people with carcinoid tumors develop symptoms of carcinoid syndrome, although this percentage varies depending on where the tumor is located. Uncomfortable flushing, typically of the head and neck, is the most common and often the earliest symptom of carcinoid syndrome. Flushing, the result of blood vessel dilation, is often triggered by emotions, by eating, or by drinking alcohol or hot liquids. The flushing may be followed by periods when the skin is bluish (cyanosis). Excessive contraction of the intestine may result in abdominal cramping and diarrhea. The intestine may not be able to absorb nutrients properly, resulting in undernutrition and fatty, foul-smelling stools.
Heart damage may occur, resulting in swelling of the feet and legs (edema). Wheezing and shortness of breath may result from obstructed airflow in the lungs. Some people with carcinoid syndrome lose interest in sex, and some men have erectile dysfunction.
When symptoms lead a doctor to suspect a carcinoid tumor, the diagnosis can often be confirmed by measuring the amount of 5-hydroxyindoleacetic acid (5-HIAA)—one of the chemical byproducts of serotonin—in the person's urine, which is collected over a 24-hour period. For at least 3 days before undergoing this test, the person refrains from eating foods that are rich in serotonin—bananas, tomatoes, plums, avocados, pineapples, eggplants, and walnuts. Certain drugs, including guaifenesin (found in many cough syrups), methocarbamol (a muscle relaxant), and phenothiazines (antipsychotics), also interfere with test results.
Different tests are used to locate carcinoid tumors. These tests include computed tomography (CT), magnetic resonance imaging (MRI), and x-rays taken after a radiopaque dye (which is visible on x-rays) is injected into an artery (arteriography). Sometimes exploratory surgery is needed to locate the tumor.
Sometimes when the diagnosis is not certain, doctors give the person a drug to try to induce flushing (called a provocative test). Currently, doctors rarely do provocative tests by giving drugs, but doctors always ask people what foods, substances, or other factors seem to induce flushing.
Radionuclide imaging or scanning is another useful test. During this test, a substance containing a radioactive tracer is injected intravenously into the body and collects in a particular organ. Most carcinoid tumors have receptors for the hormone somatostatin. Doctors can therefore inject a radioactive form of somatostatin into the blood and use radionuclide imaging to locate a carcinoid tumor and determine if it has spread. About 90% of tumors can be located using this technique. MRI or CT can be helpful in confirming whether the tumor has spread to the liver.
When a carcinoid tumor is restricted to a specific area, such as the appendix, small intestine, rectum, or lungs, surgical removal may cure the disease. If the tumor has spread to the liver, surgery rarely cures the disease but may help relieve symptoms. The tumors grow so slowly that even people whose tumors have spread often survive for 10 to 15 years.
Neither radiation therapy nor chemotherapy is effective in curing carcinoid tumors. However, combinations of certain chemotherapy drugs (streptozocin with fluorouracil and sometimes doxorubicin) may relieve symptoms.
Tamoxifen and interferon-alpha may reduce the tumor's growth.
A drug called octreotide can also relieve symptoms. Somatastatin, phenothiazines, cimetidine, and phentolamine are used to control flushing in people with carcinoid syndrome. Prednisone is sometimes given to people with carcinoid tumors of the lungs who have episodes of severe flushing.
Diarrhea may be controlled with loperamide, codeine, tincture of opium, diphenoxylate, or cyproheptadine.
Pellagra may be prevented by ensuring adequate protein in the diet and by taking niacin. Drugs that block the production of serotonin, such as methyldopa, also help prevent pellagra.
Last full review/revision July 2012 by B. Mark Evers