Neuroendocrine tumors are noncancerous (benign) or cancerous (malignant) growths that sometimes produce excessive amounts of hormone-like substances (such as serotonin), sometimes resulting in carcinoid syndrome. Carcinoid syndrome is a group of specific symptoms that occur as a result of these excessive hormones.
People with neuroendocrine tumors may have cramping abdominal pain and changes in bowel movements.
People with carcinoid syndrome usually have flushing and sometimes diarrhea.
To diagnose carcinoid syndrome, doctors measure the amount of a serotonin byproduct in the person’s urine.
Imaging tests are needed to determine tumor location.
Sometimes tumors are removed surgically.
People may need to take medications to control symptoms.
Neuroendocrine tumors (previously called carcinoid 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 neuroendocrine tumors), or rarely the testes or ovaries.
Neuroendocrine 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. Neuroendocrine 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 , which can cause the disease pellagra.
When neuroendocrine 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, neuroendocrine 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. Neuroendocrine tumors of the lungs, testes, and ovaries also cause symptoms because the substances they produce bypass the liver and circulate widely in the bloodstream.
Symptoms
People with neuroendocrine tumors can develop symptoms due to the growth of the tumor, similar to symptoms of other intestinal tumors. These symptoms are mainly cramping pain and changes in bowel movements as a result of the tumor blocking the intestine.
Carcinoid syndrome
Fewer than 10% of people with neuroendocrine tumors develop symptoms of carcinoid syndrome, although this percentage varies depending on where the tumor is located.
The most common, and often earliest symptom of carcinoid syndrome is
Uncomfortable flushing, typically of the head and neck
Flushing, the result of blood vessel widening (dilation), can be triggered by emotions, by eating, or by drinking alcohol or hot liquids. The flushing may cause the skin to have color changes ranging from red to violet to purple. In people with dark skin, flushing may cause reddening or increased darkening.
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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, which can result in symptoms of right heart failure such as swelling of the feet and legs (edema).
Wheezing and shortness of breath may result from blockage of airflow in the lungs.
Some people with carcinoid syndrome lose interest in sex, and some men have erectile dysfunction.
Diagnosis
Urine testing for 5-hydroxyindoleacetic acid
Sometimes imaging to locate a tumor
When symptoms lead a doctor to suspect a neuroendocrine tumor, the diagnosis of carcinoid syndrome 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.
Other causes of flushing, such as menopause or alcohol ingestion, need to be excluded. By asking the person questions (such as their age and about their alcohol use), doctors can usually exclude these other causes, but sometimes testing is necessary. Sometimes when the diagnosis of carcinoid syndrome is not certain, doctors give the person a medication to try to induce flushing (called a provocative test), but this method is rarely used and must be done with care.
Locating the tumor
Different tests are used to locate neuroendocrine tumors. These tests include computed tomography (CT), magnetic resonance imaging (MRI), and x-rays taken after a radiopaque contrast agent (which is visible on x-rays) is injected into an artery (angiography). Sometimes exploratory surgery is needed to locate the tumor.
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 neuroendocrine tumors have receptors for the hormone somatostatin. Doctors can therefore inject a radioactive form of somatostatin or a related substance into the blood and use radionuclide imaging to locate a neuroendocrine tumor and determine whether 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.
Treatment
Surgery to remove the tumor
Symptom control
serotonin
Surgery and other treatments
When a neuroendocrine 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. Other treatments, such as embolization, in which substances are injected into the tumor through blood vessels in the liver, also can help liver tumors. Neuroendocrine tumors grow so slowly that even people whose tumors have spread often survive for 10 to 15 years.
