What Is Carcinoid Syndrome?

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Carcinoid syndrome includes a number of symptoms that develop in people with a rare form of tumor. Carcinoid tumors are slow growing and usually form in the gut. It's when they spread—specifically to the liver—that they cause the symptoms seen in this syndrome.

This article will explore how carcinoid syndrome develops, who is at risk, and what can be done to treat it.

Coping With Carcinoid Syndrome - Illustration by Jessica Olah

Verywell / Jessica Olah

Types of Carcinoid Syndrome

Carcinoid syndrome is a term used to describe the symptoms that arise when a carcinoid tumor triggers the release of too much serotonin and other chemicals into your bloodstream. This happens in about 10% of people with carcinoid tumors, and usually only after tumors have spread to the liver or lungs from their initial locations.

Carcinoid tumors are rare tumors that develop from neuroendocrine cells that send and receive messages throughout your body. Since neuroendocrine cells can be found in virtually every tissue in the body, you can develop these tumors anywhere.

However, carcinoid tumors usually begin in either the appendix or lungs in children, and in the gastrointestinal (GI) tract in adults. Carcinoid tumors grow slowly and can spread to other organs in both children and adults, but metastasis—developing secondary cancerous growths in other parts of the body—is more common in adults with this condition.

Common locations for carcinoid tumors to originate include:

  • Small intestine
  • Appendix
  • Rectum
  • Lungs
  • Colon
  • Stomach
  • Pancreas

By the Numbers

Carcinoid tumors are so rare that only about 4 in 100,000 adults are diagnosed, and only 10% of those people go on to develop carcinoid syndrome. Many people with carcinoid tumors never experience any symptoms at all.

Carcinoid Syndrome Symptoms

It's possible to develop a carcinoid tumor and never experience symptoms, but 10% of people with carcinoid tumors develop carcinoid syndrome.

Carcinoid syndrome is defined by the symptoms it causes. These symptoms are usually signs of the faulty hormonal secretions and signals being sent out by the carcinoid tumors and malfunctioning neuroendocrine cells. Symptoms usually develop in the later stages of the disease.

The most common symptoms of carcinoid syndrome are:

Symptoms may also include:

  • Change in weight
  • Malnutrition
  • Weakness
  • Muscle aches
  • Joint pain
  • Peptic ulcers (open sores on the lining of your stomach and upper small intestine)


Carcinoid syndrome is essentially an advanced stage of a carcinoid tumor that has metastasized to more than one part of the body. By this point, these tumors begin to interfere with the body's hormonal balance and other signals affecting functioning.

Experts aren't really sure why people develop carcinoid tumors, perhaps because they are so rare. There are a few factors that seem to indicate a higher risk of developing these tumors. These include:


Carcinoid syndrome may be tricky to diagnose in some people—especially if you previously had no symptoms of a carcinoid tumor. Most carcinoid tumors develop with no symptoms at all, and they are often found by accident, such as during a surgery for another condition.

If you begin having any of the four primary symptoms listed above—especially if you fall into one of the high-risk groups—it's good to schedule an appointment with your healthcare provider. Never hesitate to seek medical attention if you are unable to breathe or you begin experiencing symptoms of heart problems.

Your healthcare provider will typically begin the examination by taking your personal and family medical history to look for any red flags that may signal the cause of your symptoms. An exact diagnosis is usually made after a number of tests that may include::

  • Blood testing
  • Imaging studies like CT (computed tomography) scans or an MRI (magnetic resonance imaging) of the chest or abdomen
  • 5-Hydroxyindoleacetic Acid (5-HIAA) testing of the urine
  • Echocardiogram (checks how blood pumps through the heart's chambers and valves)
  • A new generation of PET (positron-emission tomography) scan called a PET-DOTATATE

These tests can detect a carcinoid tumor, which may help your healthcare provider explain the symptoms you would be experiencing with carcinoid syndrome.


The main treatment for carcinoid syndrome is to remove the tumor that is triggering the condition in the first place. Many times, this means surgery to remove or reduce the size of a carcinoid tumor.

Other options for treatment, particularly when surgery is not an option, include:

  • Sandostatin (octreotide) or Somatuline (lanreotide) injections: These are both synthetic versions of somatostatin, which is a natural hormone produced by the body. 
  • Chemotherapy: Typically used in cancer treatment, chemotherapy can also target carcinoid tumor cells.
  • Targeted therapies: Biologic drugs like Afinitor (everolimus) work by regulating cell growth and significantly slow the progression of carcinoid tumors.
  • Peptide receptor radionuclide therapy (PRRT): This treatment directs high-powered radiation to the tumor cells to destroy or slow their growth while reducing the harmful effects to healthy tissues.


The prognosis of someone with carcinoid syndrome depends a lot on where the carcinoid tumor is located and to what degree it has spread. Carcinoid syndrome outcomes are usually good—and not fatal.

There are complications that can occur from carcinoid syndrome and the underlying neuroendocrine tumor. These include:


The symptoms of carcinoid syndrome can be difficult to handle, especially if they are causing severely low or high blood pressure, or other problems that can affect how well you function in a normal day.

Finding and treating tumors early is helpful in preventing carcinoid syndrome, and there are a number of strategies you can use even if you have a carcinoid tumor to try to keep the condition from getting worse.

Some tips for managing carcinoid tumors and carcinoid syndrome include:

  • Maintaining a healthy, high-protein diet
  • Avoiding alcohol and other substances that may trigger your symptoms
  • Quitting smoking
  • Reducing stress
  • Joining a support group


Carcinoid syndrome results from a carcinoid tumor—usually one in more advanced stages. There is a chance you may not know you have a carcinoid tumor until you develop severe symptoms, like those seen in carcinoid syndrome. Talk to your healthcare provider if you meet any of the risk factors for carcinoid syndrome, or if you have been diagnosed with a carcinoid tumor and start to feel worse.

A Word From Verywell

Carcinoid tumors are rare tumors that can impact your hormonal balance, causing a cascade of other problems like facial flushing, blood pressure fluctuations, and even changes to your heart rate. These tumors often develop with no symptoms at all but can progress to carcinoid syndrome once they spread through your body. If you show signs or symptoms of carcinoid syndrome, seek help from a medical professional to determine whether or not you have a carcinoid tumor.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Organization for Rare Disorders. Carcinoid syndrome.

  2. MedlinePlus. Carcinoid syndrome.

  3. National Institutes of Health. Carcinoid tumor.

  4. Johns Hopkins. Carcinoid tumor.

  5. MedlinePlus. Carcinoid tumors.

  6. Cancer Research UK. What are somatostatin analogues?

  7. Cancer Treatment Centers of America. Peptide receptor radionuclide therapy (PRRT).

By Rachael Zimlich, BSN, RN
Rachael is a freelance healthcare writer and critical care nurse based near Cleveland, Ohio.