Carcinoid tumors grow from neuroendocrine cells. These cells are found in organs throughout your body and produce and release hormones in response to nerve signals.

The most common place for carcinoid tumors to develop is the gastrointestinal tract. The second most common place is the lungs.

Carcinoid tumors are rare. According to the National Organization for Rare Disorders (NORD), 27 cases are diagnosed per million people in the United States annually. They tend to develop slowly and often don’t cause symptoms until they grow large or start producing hormones.

Keep reading to learn more about these rare tumors, including diagnosis, treatment, and outlook.

Common sites for carcinoid tumorsShare on Pinterest
Common sites for carcinoid tumors. Illustration by Jason Hoffman.

Carcinoid tumors fall into a group of tumors called neuroendocrine tumors, which develop in cells that produce hormones in response to nerve signals. These cells are found in many different organs in your body but are especially common in your digestive tract.

Carcinoid tumors are rare, and experts estimate they occur in about 1 in 25,000 adults in their lifetime. About 8,000 tumors are diagnosed in the United States each year.

They are even rarer in children. Neuroendocrine tumors are estimated to affect 2.8 children per 1 million. Bronchial carcinoid tumors are the most common childhood lung cancer.

Where carcinoid tumors develop

About 60% of carcinoid tumors arise in the gastrointestinal tract. Here’s a breakdown of the most common locations within the gastrointestinal tract according to the American Cancer Society (ACS):

  • small intestines
  • rectum
  • colon, the large intestine
  • appendix
  • stomach

The next most common location for carcinoid tumors to develop is your lungs. The lungs make up about 25% of carcinoid tumors.

Other sites they develop include:

  • thymus
  • kidneys
  • ovaries
  • pancreas
  • prostate
  • breast

In children, the most common location of carcinoid tumors is the appendix.

Carcinoid syndrome

Less than 10% of people with carcinoid tumors develop carcinoid syndrome. Carcinoid syndrome is when carcinoid tumors release hormone-like chemicals into your bloodstream. It’s most commonly due to gastrointestinal tumors that spread to the liver.

Carcinoid tumors can secrete molecules such as:

  • histamine
  • serotonin
  • tachykinins
  • prostaglandins

Carcinoid tumors tend to grow very slowly. Many people don’t have symptoms until the tumor grows large.

When tumors occur in the appendix, people tend to experience symptoms resembling appendicitis, such as abdominal pain.

Tumors in other parts of the digestive tract may cause general symptoms such as:

In the lungs, they may cause symptoms similar to pneumonia, such as:

Symptoms of carcinoid syndrome

If you develop carcinoid syndrome, you may experience:

  • flushed skin in your face and upper trunk
  • nausea and vomiting
  • diarrhea
  • purple veins on your nose and lips

Foods that contain tyramine, such as red wine or blue cheese, can provoke flushed skin.

Researchers are still working to understand why carcinoid tumors develop. Like other cancers, they occur when genetic mutations in cancer cells cause them to divide uncontrollably.

They develop most often in people ages 50 to 70 years old. However, there are cases in people as young as 10 years old.

According to NORD, men and women in the United States are affected equally. African Americans develop carcinoid tumors more often than other ethnic groups.

Carcinoid tumors don’t seem to have a link to family history. However, the genetic condition multiple endocrine neoplasia type 1 does run in families and increases the risk of developing carcinoid tumors.

According to the ACS, most lung carcinoid tumors don’t have a link to smoking, but some atypical types may have a connection.

The risk of carcinoid tumors spreading to other organs seems to be related to their size. Experts state that only about 15% of tumors smaller than 1 centimeter (cm), or 0.4 inches (in) in diameter spread to distant tissues. With tumors larger than 2 cm, or 0.8 in, 95% of them spread.

Diagnosing a carcinoid tumor is often delayed since it doesn’t usually cause symptoms in the early stages. It takes about 9.2 years from symptom onset to the diagnosis of a carcinoid tumor.

Doctors can make a diagnosis with a combination of lab tests, imaging, and a biopsy:

  • Laboratory tests: Your doctor may order blood or urine tests to check your hormone levels and monitor levels of biomarkers that are suggestive of carcinoid tumors.
  • Imaging: Imaging can help your doctor see where the tumor is and how large it’s grown. Imaging options include:
  • Biopsy: Doctors can confirm if a tumor is cancerous by taking a small tissue sample with a needle. The cells are analyzed in a laboratory to see if they’re cancerous and what type of cancer they are.

The type of PET scan is usually a PET-CT scan with gallium.

Before the scan, a healthcare professional injects gallium into your body. Gallium is a radioactive substance that travels through your body and collects in areas where cells are actively dividing. This helps doctors detect cancer cells on a scan and determine how far a cancer has spread.

Doctors sometimes diagnose carcinoid tumors after removing the appendix due to suspected appendicitis.

According to the National Cancer Institute, doctors use four primary types of treatment for carcinoid tumors:

  • Surgery: Surgery removes the tumor and the surrounding tissue. It can help keep the tumor from spreading. It may not be an option for large tumors.
  • Somatostatin analogs: Somatostatin analogs are medications that suppress hormone production. They may help manage symptoms of carcinoid syndrome and help shrink the tumor.
  • Targeted therapy: A targeted therapy called peptide receptor radionuclide therapy can target receptors on the surface of carcinoid cells called somatostatin receptors to curb their growth.
  • Chemotherapy: Chemotherapy is a drug therapy that kills cancer cells. It can also kill healthy cells in your body that replicate quickly, like skin cells and cells in your gastrointestinal tract, and cause side effects.

According to the ACS, the 5-year relative survival rate for low- and intermediate-grade gastrointestinal carcinoid tumors is as follows:

Stage5-year relative survival rate
all stages94%

Grade is a measure of how quickly doctors expect the cancer to spread. Five-year relative survival is a measure of how many people with the disease are alive 5 years later compared with people without the disease.

Below are the 5-year relative survival rates for lung carcinoid tumors based on people diagnosed between 2011 and 2017:

Stage5-year relative survival rate
all stages90%

These numbers can give you a general idea of what to expect. But your doctor can give you a better idea of your outlook based on factors such as:

  • the stage of your cancer
  • the grade of your cancer
  • your overall health
  • your age
  • how well your cancer responds to treatment

Carcinoid tumors develop in neuroendocrine cells and tend to develop very slowly. The most common place for them to develop is the gastrointestinal tract.

Many people with carcinoid tumors don’t experience any symptoms, making diagnosis difficult.

If you’re diagnosed with a carcinoid tumor, your doctor can give you the best idea of what to expect and advise you on the best treatment options.