Carcinoid Syndrome

Carcinoid syndrome may be a complication of neuroendocrine tumors (NETs). NETs are rare tumors that start in your neuroendocrine cells. Carcinoid syndrome often affects people with NETs in their lungs or digestive system. Carcinoid syndrome symptoms include diarrhea, flushing and wheezing.


Top: Female with gastrointestinal neuroendocrine tumor showing how NET of GI causes carcinoid syndrome. Below are symptoms.
Carcinoid syndrome symptoms caused by NET of GI.

What is carcinoid syndrome?

Carcinoid syndrome is a rare condition that happens if you have neuroendocrine tumors. Neuroendocrine tumors (NETs) are tumors that start in specialized cells in your neuroendocrine system.

NETs develop when your neuroendocrine cells begin to rapidly divide and multiply, creating tumors that release unusually large amounts of serotonin and other substances. When that happens, you develop carcinoid syndrome symptoms. Sometimes, a carcinoid syndrome diagnosis is the first indication you have a neuroendocrine tumor.

Very rarely, people with carcinoid syndrome have carcinoid crises, a potentially life-threatening condition that can happen if your carcinoid syndrome goes undiagnosed or untreated.

Is carcinoid syndrome common?

No, it’s not. One study suggests 1 in 5 people with neuroendocrine tumors (NETs) have carcinoid syndrome, and NETs affect about 5 in 100,000 people in the United States.


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Symptoms and Causes

What are carcinoid syndrome symptoms?

Studies suggest the most common symptoms include:

  • Uncomfortable flushing of your head and neck.
  • Wheezing and shortness of breath (dyspnea).
  • Abdominal cramping and explosive, frequent diarrhea.
  • Fatty poops that smell bad.
  • Edema or swelling of your feet and legs. This can be a symptom of heart failure.
  • Some people might lose interest in sex or have erectile dysfunction.
  • Jaundice, which is when your skin and the whites of your eyes turn yellow.
  • Dizziness or feeling faint. This can be a sign of low blood pressure.
  • Feeling like your heart is racing.

What causes carcinoid syndrome?

Carcinoid syndrome happens if you have neuroendocrine tumors. This refers to symptoms that develop from tumors in specialized cells in your neuroendocrine system that make and release hormones. While you can have NETs in your gastrointestinal tract, lungs and pancreas, carcinoid syndrome typically happens when NETs in your gastrointestinal tract or lungs flood your system with hormones.

What are the risk factors for carcinoid syndrome?

The most common risk factor is having a neuroendocrine tumor in your gastrointestinal tract or your lungs.


What are the complications of carcinoid syndrome?

Carcinoid syndrome may cause several kinds of complications, including carcinoid crises, which can be life-threatening.

Other carcinoid syndrome complications include:

  • Carcinoid heart disease: This rare but potentially life-threatening complication happens when neuroendocrine tumors release hormones that affect the linings in your heart chambers, valves and blood vessels. Carcinoid heart disease may lead to heart failure.
  • Mesenteric fibrosis: NETs may cause inflammation and scarring of your mesentery, which is a fold of tissue that attaches your intestines to the wall of your belly.
  • Depression: Carcinoid syndrome may affect your body’s ability to process tryptophan, an essential amino acid that helps to make serotonin. Serotonin is a brain chemical that manages central nervous system processes like mood, behavior and sleep.

Carcinoid crisis

Carcinoid crisis is an extremely rare but life-threatening condition. Triggers for this include surgery or other medical procedures or traumatic events like an injury from an accident. Carcinoid crisis symptoms include:

  • Wide changes in blood pressure, including low blood pressure (hypotension).
  • Severe flushing.
  • Shortness of breath (dyspnea).
  • Confusion.

People with carcinoid syndrome or a neuroendocrine tumor should carry a card listing their medical condition in case they need emergency medical care. Likewise, people with carcinoid syndrome or an NET who are planning to have surgery should make sure their providers know about their condition. Providers can administer medication before and during surgery to reduce carcinoid crisis risk.

Diagnosis and Tests

How is carcinoid syndrome diagnosed?

Healthcare providers may use the following tests to diagnose carcinoid syndrome:

  • Urine test: This test checks on certain hormone levels.
  • Physical exam and medical history: Many carcinoid syndrome symptoms are similar to other less serious illnesses. Your healthcare provider will ask questions about specific symptoms, how long you’ve had the symptoms and if your symptoms are getting worse.
  • Blood tests: These tests check on the amounts of substances that your organs and tissues release into your blood. Substance levels that spike or fall might be signs of disease.
  • Neuroendocrine positron emission tomography (PET) scan: This test tracks neuroendocrine tumors with a dye called Gallium 68 dotatate.
  • Computed tomography (CT) scan: CT scans use X-rays and a computer to produce 3D images of organs and bones.
  • Ultrasound: Ultrasounds use sound waves to develop images of organs and bones.
  • Magnetic resonance imaging (MRI): This uses a computer, radio waves and a large magnet to create images of the inside of your body.
  • Endoscopy: For this test, a provider inserts a long thin tube with a camera and a light into your body.


Management and Treatment

How is carcinoid syndrome treated?

Neuroendocrine tumors cause carcinoid syndrome, so treating the tumors also treats the syndrome.

Those treatments include:

  • Surgery: Surgery to remove or reduce the size of the neuroendocrine tumors.
  • Somatostatin analogs: Somatostatin analogs are drugs that may stop your body from making too many hormones. This may slow down the growth of the tumor when cancer cells spread to other parts of your body.
  • Targeted therapy: Targeted therapy is a type of treatment that uses drugs that target certain genes or proteins to kill cancer cells.
  • Chemotherapy: This treatment uses drugs that destroy cancer cells.
  • Embolization: Embolization kills tumors by blocking or closing a blood vessel that feeds the tumor


Can carcinoid syndrome be prevented?

No, it can’t be prevented. Carcinoid syndrome is linked to neuroendocrine tumors, and as there isn’t a known way to prevent NETs, there’s no way to prevent its symptoms.

Living With

How do I take care of myself?

If you have carcinoid syndrome, you probably also have a neuroendocrine tumor. If you have carcinoid syndrome symptoms, tell your healthcare provider. They’ll be able to assess your situation and recommend tests to determine if you have an NET.

The three main carcinoid syndrome symptoms are flushing, wheezing and diarrhea. Here are some suggestions for managing the main symptoms:

  • Flushing: Flushing is your nervous system’s reaction to physical or emotional stress. You can ease flushing by taking deep breaths, cooling your face and chest with a damp cloth or getting some fresh air. Avoiding alcohol can reduce flushing.
  • Wheezing: Try drinking herbal tea, or using an inhaler or a vaporizer to help your breathing. If you smoke, try to stop. Smoking irritates your airways.
  • Diarrhea: If diarrhea is an issue, talk to your healthcare provider about ways to reduce its frequency and severity. There are medications specifically designed to slow down diarrhea from carcinoid syndrome.

When should I see my healthcare provider?

You should see your healthcare provider if your carcinoid syndrome symptoms get worse. If you’re receiving treatment for a neuroendocrine tumor, let them know if you notice changes in your body that feel like NET symptoms. These changes might be unrelated to your NET diagnosis, and the best way to be sure of that is to talk to your provider. You should also contact your provider if your symptoms or treatment side effects become worse.

When should I go to the emergency room?

Carcinoid syndrome symptoms get worse over time if untreated and can become a life-threatening condition called carcinoid crisis. Go to the emergency room if:

  • You’re having heart palpitations or chest pain.
  • You have severe diarrhea that’s lasted several days.
  • You have severe stomach pain.
  • You feel faint.
  • You have acute flushing of your face, neck and chest.

What questions should I ask my healthcare provider?

Carcinoid syndrome might be a sign you have a neuroendocrine tumor. While you’ll have questions about carcinoid syndrome, you’ll probably have more questions about NETs. Here are some questions you might want to ask your healthcare provider:

  • If I have carcinoid syndrome, how do I find out if I have a neuroendocrine tumor?
  • If I have a tumor, where is it located in my body?
  • What’s the treatment for my tumor?
  • What are the treatment side effects?
  • Can you cure the neuroendocrine tumor that caused my carcinoid syndrome?
  • Can carcinoid syndrome come back after you treat my neuroendocrine tumor?

A note from Cleveland Clinic

Carcinoid syndrome is a rare condition that happens if you have a neuroendocrine tumor or NET. In most cases, people with carcinoid syndrome already know they have an NET. Other times, a carcinoid syndrome diagnosis is how people learn they have a neuroendocrine tumor. You can get treatment for NETs. Learning you have carcinoid syndrome is your first step toward finding out if you have cancer and if you do, how to treat it. If you have a carcinoid syndrome diagnosis, ask your healthcare provider about next steps to confirm potential NETs.

Medically Reviewed

Last reviewed on 06/14/2023.

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