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Carcinoid tumors are a rare, slow-growing type of cancer that can be cured if caught early, but is difficult to diagnose.

Most carcinoid tumors start in the gut, including the intestines, appendix, rectum, colon, stomach, and pancreas. They account for about one-third of all tumors of the small intestine and almost 50% of all malignant tumors of the small intestine. Yet these tumors can also be found in the lungs, ovary, and elsewhere.

Carcinoid tumors are a type of neuroendocrine tumor, which means they come from cells of the nervous and endocrine system, and can produce hormones. When they secrete excess hormones such as histamine and serotonin, they can cause symptoms such as flushing, stomach cramps, and diarrhea. This is called carcinoid syndrome.

Like most other types of cancer, carcinoid tumors are most easily treated when found early. In fact, in the early stages they can often be completely cured through surgery. Most carcinoid tumors grow and spread very slowly. But because these tumors often don't cause any symptoms for many years, early detection can be tricky.

Signs and Symptoms of a Carcinoid Tumor

When carcinoid tumors do cause symptoms, they may be vague, or may be similar to symptoms of other medical conditions.

Some gastrointestinal carcinoid tumors can cause symptoms such as abdominal pain, constipation, bleeding, or cramping. The lung carcinoids can cause infection, pneumonia, or chronic cough.

Carcinoid tumors can also lead to two conditions: Carcinoid syndrome and Cushing's syndrome.

Symptoms of carcinoid syndrome include diarrhea, flushing of the skin, wheezing, shortness of breath, abdominal cramps, and heart palpitations.

Symptoms of Cushing's syndrome can include weight gain, muscle weakness, thinning of the skin, increased facial and body hair, high blood sugar, and high blood pressure.

"The biggest obstacle in diagnosing carcinoid tumors is not thinking of them," says Richard Warner, MD, professor of medicine at the Mount Sinai School of Medicine and medical director of the Carcinoid Cancer Foundation. "Because carcinoid tumors are not so common, doctors may not think of them as a possibility when they see these symptoms."

Risk Factors for Carcinoid Tumors

Researchers are still learning about carcinoid tumors and what causes them. There are a few known risk factors for carcinoid tumors, and most are not factors you can control or change.

  • Genetic syndromes. People with a rare genetic syndrome called Multiple Endocrine Neoplasia, type 1 (MEN1) have a higher risk of certain tumors, including carcinoid tumors. Those with a disease called neurofibromatosis type 1 are also at higher risk for developing carcinoid tumors.
  • Gender. Women may be at slightly higher risk of developing carcinoid tumors. Researchers aren't sure why.
  • Race. Gastrointestinal carcinoid tumors are more common in African-American men and women than in Caucasians. But lung carcinoid tumors are more common in Caucasians than in people of other races.
  • Stomach conditions. Those who have a stomach condition that reduces the amount of acid in the stomach and damages the stomach have a higher risk of carcinoid tumors in the stomach.
  • Smoking. Smokers may be more likely to have certain types of lung carcinoid tumors. A recent study in Europe also found that smoking may double the risk of having a carcinoid tumor in the small intestine. But more research is needed to confirm these results.

Signs of Carcinoid Syndrome

Can you spot the symptoms of Carcinoid syndrome?
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