Carcinoid tumors are an unusual, slow-growing type of cancer that can arise in several places throughout your body. They most commonly appear in the gastrointestinal tract (appendix, stomach, small intestine, colon, rectum) and in the lungs. But, carcinoid tumors can also begin in other organs, including the ovaries and testes.

These rare tumors differ from more common cancers in several ways. They grow slowly and rarely cause any signs or symptoms until late in the disease. Even under a microscope a carcinoid tumor can appear to be noncancerous (benign), even though it may have already spread. Carcinoid tumors can also produce and release hormones into your body that cause signs and symptoms, such as diarrhea or skin flushing.

Because of the lack of early signs and symptoms, diagnosing carcinoid tumors early can be challenging. In many cases, carcinoids are found during a test or procedure for an unrelated condition. Once they are detected, treatment usually involves surgery to remove the carcinoid tumor. In people whose carcinoid tumor has not spread, survival rates after surgery are excellent.

In many cases, carcinoid tumors don't cause any signs or symptoms. When they do occur, signs and symptoms are usually vague and depend on the location of the tumor:

• Gastrointestinal carcinoid tumors. If you have a carcinoid tumor in your stomach, you may experience some abdominal pain. In the small intestine and colon, carcinoids sometimes cause changes in bowel movements, abdominal pain or, in rare cases, blockage of the intestines. Carcinoid tumors of the rectum may result in rectal bleeding and pain.
• Lung carcinoid tumors. In the lungs, carcinoid tumors can cause recurrent pneumonia, cough or chest pain. Lung carcinoid tumors can also cause you to cough up blood.

No one knows what causes carcinoid tumors. Carcinoid tumors develop from cells in the neuroendocrine system, a part of your body that has many functions, including production of certain hormones. These cells also have characteristics similar to nerve cells.

In the digestive system, neuroendocrine cells help to regulate the release of digestive juices, control the movement of food in the stomach and intestines, and may help control the growth of other types of digestive system cells. In the lungs, neuroendocrine cells help control air and blood flow and may help control growth of other types of lung cells.

Carcinoid tumors develop when some of these neuroendocrine cells undergo changes that cause them to grow too much.

Carcinoid tumors start out very small and grow slowly. Researchers have found some tiny tumors in neuroendocrine cells, called tumorlets, which look like miniature carcinoids. What causes some tumors to grow and cause signs and symptoms, while others remain small and harmless, is unclear.

Although carcinoid tumors can occur at any age, they're more common in older people. Children rarely develop these types of tumors. Other risk factors for carcinoid tumors include:

• Sex. Carcinoid tumors affect women more often than men.
• Family history. Children who have a parent with carcinoid tumors are at an increased risk of developing these tumors. A family history of multiple endocrine neoplasia type 1 (MEN 1) syndrome also is a risk factor for carcinoid tumors. In MEN 1, multiple tumors occur in glands of the endocrine system.
• Smoking. Although smoking is not associated with most carcinoid tumors, smoking may be linked to some atypical lung carcinoids.
• Other medical conditions. Conditions that affect the stomach's ability to produce acid, such as gastritis or pernicious anemia, can increase your risk of gastrointestinal carcinoids.

Because carcinoid tumors often don't cause any early signs or symptoms, it can be difficult to know when you need to seek medical care. Symptoms that could be caused by carcinoid tumors include the following:

• Redness or a feeling of warmth in your face and neck (skin flushing)
• Diarrhea that is persistent and unrelenting
• Difficulty breathing
• Wheezing
• Fast heartbeat
• Fatigue
• Swelling of your feet and ankles
• Pain or a feeling of fullness in your abdomen

The above signs and symptoms are not specific to carcinoid tumors, and they are much more commonly caused by other conditions. If you have persistent or unrelenting symptoms, see your doctor.

In some cases, these signs and symptoms may be related to carcinoid syndrome, a rare condition that can develop as a result of carcinoid tumors.

Because carcinoid tumors grow slowly and rarely cause signs or symptoms, doctors often discover carcinoids by chance during a test or procedure for an unrelated condition. No screening test is available for carcinoid tumors, nor is screening routinely necessary because the disease is so rare. If your family has a strong history of MEN 1, your doctor should monitor your condition carefully, watching for the possible development of a carcinoid tumor.

If your doctor suspects you have a carcinoid tumor, he or she may recommend the following tests:

• Blood test. If you have a carcinoid tumor, your blood may contain high levels of the protein chromogranin A.
• Urine test. People with carcinoid tumors may secrete excess levels of a chemical called 5-HIAA in their urine.
• Computerized tomography. Doctors often use computerized tomography (CT) scans to confirm a carcinoid tumor diagnosis, pinpoint the tumor's location and determine if it has spread.
• Biopsy. A biopsy is the only test that can definitely confirm the presence of any cancer, including a carcinoid tumor. Your doctor may do a biopsy with just a needle or by some type of surgical procedure. He or she will determine which method is best based on your individual circumstances.

Carcinoid tumors aren't the same as other tumors, such as adenocarcinomas (malignant tumors in cells that produce mucous) and adenomas (benign tumors in mucous-producing cells). Because carcinoids' slow rate of growth, course of disease, treatment and outlook for survival are different from other tumors, it's important that you receive an accurate diagnosis.

Like the neuroendocrine cells they come from, carcinoid tumors can secrete hormones and other chemicals into your body. Carcinoid tumors may produce serotonin, a chemical that helps regulate your mood, appetite and sensory perception. The chemicals from carcinoids can cause a number of medical problems. These and other complications of carcinoid tumors include:

• Carcinoid syndrome. Carcinoid syndrome is a result of the hormones made by carcinoid tumors. The condition produces redness or a feeling of warmth in your face and neck (skin flushing), diarrhea and difficulty breathing, among other signs and symptoms.

  When carcinoid tumors secrete chemicals, your liver usually eliminates them before they have a chance to circulate throughout your system. Most people who experience carcinoid syndrome have an advanced, metastatic carcinoid tumor that has spread to the liver, where the chemicals released have a better chance of getting into the bloodstream. Exceptions to this are carcinoids in the ovaries and the lungs, which can produce signs and symptoms of carcinoid syndrome before the disease has spread.

• Heart problems. The hormones from carcinoids may cause thickening of the lining of your heart's chambers, valves and blood vessels. It's more common for the right side of the heart to be affected than the left. This condition often causes the valve between the upper and lower chambers on the right side of your heart to leak (tricuspid regurgitation), allowing blood to flow backward. It also leads to narrowing of the pulmonary valve — the valve that keeps blood from flowing back from your pulmonary artery to the lower right chamber of your heart (right ventricle) when the right ventricle relaxes between contractions. (Your pulmonary artery is the blood vessel that carries oxygen-poor blood from the right ventricle to your lungs.) If left untreated, these conditions may result in enlargement of your heart (cardiomegaly) and heart failure.
• Cushing's syndrome. A carcinoid tumor in your lung may produce an excess of adrenocorticotropic hormone (ACTH), which can lead to overproduction of the hormone cortisol. This is known as Cushing's syndrome, a condition that occurs when your body is exposed to high levels of cortisol for a prolonged period of time.
• Acromegaly. Carcinoid tumors in the lungs can cause your body to produce too much growth hormone. This may result in the rare hormonal disorder acromegaly, which causes your bones to increase in size, including those of your hands, feet and face.
• Intestinal obstruction. Large carcinoid tumors in the intestines can block food and fluid from passing through your small intestine or colon. If left untreated, intestinal obstruction can cause parts of your intestine to die. This tissue death can lead to perforation of the intestine, severe infection and shock.
• Peptic ulcers. Some carcinoid tumors (often those in the stomach) produce large amounts of the hormone gastrin that causes your stomach to produce excess acid. This can lead to severe stomach ulcers, bleeding and even perforation of the stomach — a condition known as Zollinger-Ellison syndrome.

Treatment of a carcinoid tumor depends on whether it has spread to other parts of your body (metastasized). If your cancer has not spread, the tumor can often be surgically removed and no further treatment is necessary.

If surgery isn't an option because your cancer is too widespread, your doctor may recommend other treatments for your tumors. These treatments could include:

• Slowing the tumor's growth. Monthly injections of the drug octreotide (Sandostatin) may slow the growth rate of your carcinoid tumor. Octreotide controls flushing and diarrhea in most people with carcinoid syndrome. Side effects of octreotide include abdominal pain and bloating, diarrhea and nausea; these symptoms may subside with time. Some people can't tolerate the side effects of octreotide and must stop taking the drug. In addition, the drug is very expensive.
• Stopping blood supply to the tumor. In a procedure called hepatic artery embolization, a doctor inserts a catheter through a needle near your groin and threads it up to the main artery that carries blood to your liver (hepatic artery). The doctor releases particles to clog the hepatic artery, cutting off the blood supply to cancer cells that have spread to the liver. Often, these particles are given along with chemotherapy, so the chemotherapy is also delivered directly to the tumor. The healthy liver cells survive by relying on blood from other blood vessels. Hepatic artery embolization can be risky, especially in people with liver disease, and the procedure is typically only performed in specialized medical centers. Discuss the benefits and risks with your doctor.
• Killing cancer cells with heat. Radiofrequency ablation delivers heat through a needle to the cancer cells in the liver, causing the cells to die. Radiofrequency ablation might be an option if you have a small number of liver metastases that are small in size. Radiofrequency ablation is generally safe, though there's a small risk of blood loss and infection.
• Chemotherapy. Chemotherapy drugs may shrink carcinoid tumors. What side effects you may experience will depend on which chemotherapy drugs you receive. Discuss your chemotherapy regimen with your doctor.

It's difficult to prevent carcinoid tumors because you can't avoid most of the known risk factors, such as family history, age and sex. Quitting smoking may reduce your risk of developing some types of carcinoids.

Everyone has his or her own way of coping with cancer. But, you don't have to do it alone. If you have questions or would like guidance, talk with a member of your health care team. Also consider the following steps to help you deal with your diagnosis:

• Find out all you can about carcinoid tumors. Ask your doctor questions about your condition. Ask members of your health care team to recommend resources where you can get more information. The more you know about your condition, the better you're able to participate in decisions about your care.
• Talk to others. Support groups for people with carcinoid tumors put you in touch with others who have faced the same challenges you're facing. Ask your doctor about groups in your area. Carcinoid tumors are rare, though, so you may need to connect with people outside your immediate area.
• Take care of yourself. Do what you can to maintain a healthy lifestyle. Choose healthy meals with plenty of fruits and vegetables. When you feel up to it, work light exercise into your daily routine. Cut extra stress out of your life when possible. Get plenty of sleep so that you feel rested when you wake up. Take care of your body and mind so that you're better able to stick to your cancer treatment plan.