Encyclopedia / C / Carcinoid Syndrome

Carcinoid Syndrome


Carcinoid syndrome is caused by an uncommon intestinal or lung tumor, called a carcinoid tumor, that secretes excess quantities of hormones.


Symptoms associated with carcinoid tumors (also called argentaffinomas) include attacks of severe flushing of the skin lasting from minutes to days, watery diarrhea, abdominal cramps, bronchoconstrictive attacks, and edema (swelling) of the head and neck.

Symptoms are caused by histamine, serotonin, prostaglandins, and other biologically active substances secreted by the tumor. The serotonin is metabolized to 5-hydroxyindoleacetic acid (5-HIAA), which is then found in urine.

They are the most common tumors of the appendix, occurring in about one out of every 300 appendectomies. They make up 30 percent of small bowel tumors but less than 2 percent of all gastrointestinal malignancies.

In their early stages, carcinoid tumors are highly treatable and curable. They are usually slow growing and behave like benign tumors. The risk of metastasis is related to the size of the primary tumor.

Carcinoids may occur in multiple sites (about 20 percent have multiple tumors), and, except for those of rectal origin, may produce an endocrine substance called serotonin.

In most cases, there are no symptoms, so many carcinoid tumors are discovered incidentally during abdominal operations performed for other reasons.

The survival of most people with carcinoid tumors is quite good, although symptoms may develop when the tumor cannot be removed, when it recurs after treatment or when there is metastatic disease.


Symptoms are unusual in the early stages. When symptoms do occur, the tumor has already spread in 90 percent of patients.

The most common symptoms are flushing, diarrhea, wheezing, facial edema (swelling) and periodic abdominal pain.


Metastatic carcinoid tumors may be diagnosed by the clinical findings and by elevated levels of 24-hour urinary 5-hydroxyindolacetic acid (5-HIAA), a metabolic product of the serotonin produced by the tumor.

False positive 5-HIAA tests can be caused by foods such as bananas, avocados and pineapple, and by certain drugs.


Drugs that block the action of serotonin and/or histamine may be successful in relieving the symptoms. Diarrhea and abdominal cramping may be treated with hydration and diphenoxylate with atropine (Lomotil). Octreotide (a somatostatin agonist) may also be helpful.

Appendiceal, rectal, and small bowel carcinoids are treated surgically. Liver and lung carcinoids may also be treated surgically in some cases. Chemotherapy is used for patients with progressive advanced-stage disease.


What is causing the symptoms?

What is the site of the carcinoid tumor?

How are carcinoids different from the usual cancers of the bowel?

Has it metastasized?

What is the urine 5-HIAA level?

Can medication be taken to block the serotonin?

Is surgery indicated?

What is the prognosis?