Carcinoid Syndrome (Carcinoid Tumor)

  • Medical Author:
    Dennis Lee, MD

    Dr. Lee was born in Shanghai, China, and received his college and medical training in the United States. He is fluent in English and three Chinese dialects. He graduated with chemistry departmental honors from Harvey Mudd College. He was appointed president of AOA society at UCLA School of Medicine. He underwent internal medicine residency and gastroenterology fellowship training at Cedars Sinai Medical Center.

  • Medical Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

woman with abdominal pain

What is a carcinoid tumor?

A carcinoid tumor is a tumor that develops from enterochromaffin cells. Enterochromaffin cells are hormone- and chemical-producing cells that normally are found in the small intestine, appendix, colon, rectum, bronchi, pancreas, ovaries, testes, bile ducts, liver, as well as other organs. Enterochromaffin cells produce many types of substances for example, histamine, serotonin, dopamine, tachykinins, and other chemicals that have profound effects on the circulatory system (heart and blood vessels), the gastrointestinal tract, and the lungs. These substances are therefore called vasoactive amines. For example, serotonin can cause diarrhea, histamine wheezing, and tachykinins flushing due to dilation of blood vessels.

Since carcinoid tumors develop from enterochromaffin cells, they frequently retain the capability of producing the same hormones, often in large quantities. When these hormones circulate in the blood, they can cause symptoms of carcinoid syndrome, which is discussed later.

The important characteristic of carcinoid tumors that sets them apart from other gastrointestinal tract tumors is their potential to cause the carcinoid syndrome. Most other gastrointestinal tract tumors (such as colon cancers or small bowel lymphomas) cause symptoms primarily due to their local effects on the intestines such as abdominal pain, intestinal bleeding, and intestinal obstruction. Although carcinoid tumors may also cause these local symptoms, they may also produce and release the substances that cause the carcinoid syndrome. Often, symptoms of the carcinoid syndrome can be more devastating than the local symptoms.

What is carcinoid syndrome?

The carcinoid syndrome is a combination of symptoms caused by the hormones and other chemical substances released by the tumors into the blood stream. The symptoms of the carcinoid syndrome vary depending on which hormones are released by the tumors. The common hormones released are serotonin, bradykinin (a molecule produced by enzymes at the site of an injury and then binds to receptors to cause pain), histamine, and chromogranin A (a general marker for neuroendocrine tumors). Typical carcinoid symptoms include:


Flushing is the most common symptom of carcinoid syndrome. An estimated 90% of the patients have flushing some time during their illness. Flushing is characterized by redness or purple discoloration of face and neck (or upper body) accompanied by a warm sensation. Episodes of flushing typically occur suddenly, either spontaneously or brought on by emotional stress, physical stress, or drinking alcohol. Episodes of flushing can last minutes to hours. Flushing can be accompanied by palpitations, low blood pressure, or fainting if blood pressure becomes too low to supply blood to the brain. Rarely, flushing can be accompanied by high blood pressure. Substances responsible for flushing have not been clearly identified; possible candidates include serotonin, bradykinin, and substance P.


Diarrhea is the second most common symptom of carcinoid syndrome. An estimated 75% of patients with carcinoid syndrome have diarrhea. Diarrhea often occurs with flushing but also can occur alone. Diarrhea in the carcinoid syndrome is most likely caused by the hormone serotonin. Medications that block the action of serotonin such as ondansetron (Zofran) often alleviate the diarrhea. Sometimes diarrhea in the carcinoid syndrome can be due to a local effect of the tumor partially obstructing the small intestine.

Heart disease

Heart disease occurs in an estimated 50% of patients with the carcinoid syndrome. Carcinoid syndrome typically causes scarring and stiffness of the tricuspid and pulmonic valves of the right side of the heart. Stiffness of these two valves decreases the ability of the heart to pump blood from the right ventricle to the lungs and to the rest of the body and leads to heart failure. Typical symptoms of heart failure include an enlarged liver (due to the backup of blood returning to the failing heart which is unable to pump all of the blood returning to it), swelling of the feet and ankles (edema), and swelling of the abdomen due to fluid accumulation (ascites). The damage to the tricuspid and pulmonic valves of the heart in the carcinoid syndrome is most likely caused by prolonged exposure to high levels of serotonin in the blood.

Carcinoid crisis

Carcinoid crisis is a dangerous condition that can occur at the time of surgery. It is characterized by a sudden and profound drop in blood pressure causing shock, sometimes accompanied by an abnormally fast heart rate, high blood glucose, and severe bronchospasm. Carcinoid crisis can be fatal. The best way to prevent carcinoid crisis is to treat patients undergoing surgery with somatostatin (see below) before surgery begins.


Wheezing occurs in approximately 10% of the patients with carcinoid syndrome. It is a result of bronchospasm (constriction of the bronchial airways) caused by hormones released by the carcinoid tumors.

Abdominal pain

Abdominal pain is common in patients with carcinoid syndrome. The pain may be due to tumor metastases in the liver, tumor invading neighboring tissues and organs, or tumor causing bowel obstruction (please see small bowel carcinoid tumors below).

Medically Reviewed by a Doctor on 7/27/2015

Subscribe to MedicineNet's Newsletters

Get the latest health and medical information delivered direct to your inbox!

By clicking Submit, I agree to the MedicineNet's Terms & Conditions & Privacy Policy and understand that I may opt out of MedicineNet's subscriptions at any time.

  • Carcinoid Syndrome - Experience

    Describe your experience with carcinoid syndrome

    Post View 11 Comments
  • Carcinoid Syndrome - Signs and Symptoms

    What were the signs and symptoms associated with your carcinoid tumor or syndrome?

    Post View 5 Comments

Health Solutions From Our Sponsors