By Jennifer Sabour, MS 

 Medically reviewed by Rony Kampalath, MD

Carcinoid tumors are rare, slow-growing tumors that can arise in several places throughout the body.¹ Carcinoid tumors are a subset of tumors called neuroendocrine tumors (NETs) that usually begin in the digestive tract (stomach, appendix, small intestine, duodenum, colon, or rectum) or in the lungs. In some cases, carcinoid tumors can begin in other parts of the body, such as the testicles or ovaries.

While carcinoid tumors are cancerous, they are unique in that they are considered to be "cancer in slow motion."¹ In rare cases, carcinoid tumors may metastasize (spread to other areas of the body).

Verywell / Jessica Olah

If you have a carcinoid tumor, you may have it for years and never know it. Since carcinoid cancers grow very slowly, they are usually not diagnosed until ages 55–65.

What Is Carcinoid Syndrome?

Carcinoid syndrome occurs when a carcinoid tumor releases specific chemicals, such as serotonin, into your bloodstream. Fewer than 10% of people with carcinoid tumors have or develop carcinoid syndrome.² However, this statistic may vary based on the location of the tumor and when it is diagnosed by a doctor.

Among carcinoid tumors, gastrointestinal tumors make up 60% of all neuroendocrine tumors.² The incidence (frequency of disease) of carcinoid tumors is greater in Black people than in white people. Black men also have a higher risk of developing carcinoid tumors than Black women, although these factors are understudied.

Carcinoid Tumor Symptoms

The symptoms of carcinoid tumor depend on where it is located in the body and where chemicals are secreted in the bloodstream.¹ If the carcinoid tumor is located in the digestive tract, symptoms may include:³

• Pain in the abdomen

• Nausea, vomiting, or constipation

• Diarrhea

• Rectal bleeding

• Rectal pain

If the carcinoid tumor is in the lungs, symptoms may include:

• Trouble breathing

• Chest pain

• Wheezing

• Redness or a feeling of warmth on the neck (skin flushing)

• Pink or purple marks on the neck that look like stretch marks

Causes

Scientists do not know what causes carcinoid tumors. However, cancers occur when cells develop mutations in their deoxyribonucleic acid (DNA), humans' hereditary material. The mutations enable cells to grow and divide uncontrollably, whereas healthy cells would normally die over time.⁴ As these mutated cells accumulate, they grow into clumps of cells known as tumors and may invade nearby tissues or metastasize.

However, some studies have shown that patients with a rare condition called multiple endocrine neoplasia type 1 (MEN1) have a higher chance of developing bronchial and intestinal carcinoid tumor.⁵ This suggests that the MEN1 gene may play a role in carcinoid tumors of the lung and digestive tract.

Diagnosis

Small carcinoid tumors may be difficult to detect and therefore difficult to diagnose. Often, these tumors are detected during surgery or in an exam for another condition. However, there are tests that can be used to detect carcinoid tumors, including:¹

• X-rays and diagnostic scans: These include a chest X-ray, computed tomography (CT) scan, magnetic resonance imaging (MRI) scan, and gallium-68 dotatate PET/CT (ga-68 dotatate). The ga-68 dotatate is a newer-generation scan that is now used to detect all types of neuroendocrine tumors.

• Blood test: A blood test may show an increased level of serotonin, a hormone responsible for mood regulation. Recent studies also suggest that serotonin is a growth factor for several cancer types.⁶ A blood test can also show high levels of chromogranin A (CgA), which is a substance made by most carcinoid tumors.⁷

• Urine test: If you or someone you know have a carcinoid tumor that is making too much hormone, it may show up as a type of acid in your urine called 5-HIAA (5-hydroxy indole acetic acid). This is a waste product of serotonin.⁸

• Biopsy: A biopsy is a surgical procedure to test a sample of tissue from the carcinoid tumor and look at it under a microscope. It can sometimes be done by using a flexible scope to look inside your body. This procedure is called endoscopy. If a tumor is found, your doctor may take a sample of the tissue for diagnosis.

• Octreotide scan: This is a special type of scan that can detect carcinoid tumors. This scan is taken after injection of a radioactive substance known as indium-111 (In 111) that is picked up by carcinoid tumor cells. It is generally more sensitive to X-rays and diagnostic scans.⁹

Treatment

If small carcinoid tumors have not spread yet, the best treatment is surgery. If the tumor has become too big or has metastasized, other treatments that are available include:¹⁰

• Chemotherapy: This treatment uses strong drugs to kill tumor cells. It can be given through a vein or taken as a pill. Chemotherapy is sometimes recommended for treating advanced carcinoid tumors that can't be removed with surgery.

• Partial surgery: This is essential if a tumor is too big to be taken out. Partial surgery may help treatments work better.

• Medications to control excess hormones: Some medications can be used to block hormones secreted by carcinoid tumors. This may help reduce symptoms and slow tumor growth.

• Liver treatment: Carcinoid tumors commonly spread to the liver. Common liver treatments include radiofrequency ablation, which delivers heat treatments that cause carcinoid tumor cells in the liver to die. Another treatment is cryoablation, which uses cycles of freezing and thawing to kill cancer cells.

Prognosis

According to the American Cancer Society (ACS), the five-year relative survival rate of people in the United States who are diagnosed with gastrointestinal (GI) carcinoid tumor is about 90%.¹¹ However, this percentage may change depending on how far the cancer has spread, a person's age, overall health, and available treatments.

The SEER (Surveillance, Epidemiology, and End Results) database tracks the five-year relative survival rates of people with GI carcinoid tumors based solely on how far the cancer has spread. These categories include localized, regional, and distant stages, which are:

• Localized: The cancer has not spread beyond the organ in which it started in (stomach, small intestine, duodenum).

• Regional: The cancer has grown through the wall of the organ where it began and entered tissues such as fats, muscles, and ligaments.

• Distant: The cancer has metastasized, or spread out to major parts of the body including the lungs, bones, and liver.

Data collected 2011–2017

Coping

Each person with cancer develops their own way of coping. But you don't have to do it alone. If you have questions or would like guidance, talk to a healthcare professional. Also consider the following steps to help you deal with your diagnosis:³

• Find out enough about carcinoid tumors to make decisions about your care: Ask your doctor questions about your condition. The more open and honest conversations with your healthcare provider, the better informed you'll be in taking the necessary steps to manage and treat your condition.

• Talk to others with cancer: Cancer support groups can help put you in contact with people who have faced or are facing the same challenges. Ask your doctor about cancer support groups in your area. You may also contact your local chapter of the ACS or the Carcinoid Cancer Foundation.

• Control what you can about your health: A cancer diagnosis can make you feel as if you have no control over your health. But you can take steps to maintain a healthy lifestyle so that you'll better cope with your cancer treatment.

• Eat healthy meals and get enough exercise: Eat plenty of fruits and vegetables that are high in vitamin C, which can help boost your immune system.¹² When you feel up to it, work light exercise into your daily routine. Cut stress when possible and get plenty of sleep so that you feel rested when you wake up. These are simple but important steps to improve your mental well-being and overall health.

Summary

Carcinoid tumors are rare, slow-growing tumors that are part of a subset called neuroendocrine tumors (NETs). They can arise in several places throughout the body, such as the digestive tract or in the lungs. Symptoms vary depending on location of the tumor and where chemicals are released in the bloodstream.

Small carcinoid tumors may be difficult to detect and, therefore, diagnose. However, once found, there are many options for treatment. Treatment options include chemotherapy, surgery, medications, and liver treatment (if the tumor has spread to the liver).

The survival rate for those with carcinoid tumors is promising, especially if the cancer has not spread.

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