A gastrointestinal carcinoid tumor is cancer that forms in the lining of the gastrointestinal tract.

The gastrointestinal tract includes the stomach, small intestine, and large intestine. These organs are part of the digestive system, which processes nutrients ( vitamins, minerals, carbohydrates, fats, proteins, and water) in foods that are eaten and helps pass waste material out of the body. Gastrointestinal carcinoid tumors develop from a certain type of hormone -making cell in the lining of the gastrointestinal tract. These cells produce hormones that help regulate digestive juices and the muscles used in moving food through the stomach and intestines. A gastrointestinal carcinoid tumor may also produce hormones. Carcinoid tumors that start in the rectum (the last several inches of the large intestine) usually do not produce hormones.

Gastrointestinal carcinoid tumors grow slowly. Most of them occur in the appendix (an organ attached to the large intestine), small intestine, and rectum. It is common for more than one tumor to develop in the small intestine. Having a carcinoid tumor increases a person’s chance of getting other cancers in the digestive system, either at the same time or later.

Health history can affect the risk of developing gastrointestinal carcinoid tumors.

Risk factors include the following:

• Having a family history of multiple endocrine neoplasia type 1 (MEN1) syndrome.
• Having certain conditions that affect the stomach’s ability to produce stomach acid, such as atrophic gastritis, pernicious anemia, or Zollinger-Ellison syndrome.
• Smoking tobacco.

A gastrointestinal carcinoid tumor often has no signs in its early stages. Carcinoid syndrome may occur if the tumor spreads to the liver or other parts of the body.

The hormones produced by gastrointestinal carcinoid tumors are usually destroyed by blood and liver enzymes. If the tumor has spread to the liver, however, high amounts of these hormones may remain in the body and cause the following group of symptoms, called carcinoid syndrome:

• Redness or a feeling of warmth in the face and neck.
• Diarrhea.
• Shortness of breath, fast heartbeat, tiredness, or swelling of the feet and ankles.
• Wheezing.
• Pain or a feeling of fullness in the abdomen.

These symptoms and others may be caused by gastrointestinal carcinoid tumors or by other conditions. A doctor should be consulted if any of these symptoms occur.

Tests that examine the blood and urine are used to detect (find) and diagnose gastrointestinal carcinoid tumors.

The following tests and procedures may be used:

• Complete blood count: A procedure in which a sample of blood is drawn and checked for the following:
  • The number of red blood cells, white blood cells, and platelets.
  • The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.
  • The portion of the sample made up of red blood cells.
• Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.
• Blood chemistry studies: A procedure in which a blood sample is checked to measure the amounts of certain substances, such as hormones, released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease in the organ or tissue that produces it. The blood sample is checked to see if it contains a hormone produced by carcinoid tumors. This test is used to help diagnose carcinoid syndrome.
• Twenty-four-hour urine test: A test in which a urine sample is checked to measure the amounts of certain substances, such as hormones. An unusual (higher or lower than normal) amount of a substance can be a sign of disease in the organ or tissue that produces it. The urine sample is checked to see if it contains a hormone produced by carcinoid tumors. This test is used to help diagnose carcinoid syndrome.

Certain factors affect prognosis (chance of recovery) and treatment options.

The prognosis (chance of recovery) and treatment options depend on the following:

• Whether the cancer can be completely removed by surgery.
• Whether the cancer has spread from the stomach and intestines to other parts of the body, such as the liver or lymph nodes.
• The size of the tumor.
• Where the tumor is in the gastrointestinal tract.
• Whether the cancer is newly diagnosed or has recurred.

Treatment options also depend on whether the cancer is causing symptoms. Most gastrointestinal carcinoid tumors are slow-growing and can be treated and often cured. Even when not cured, many patients may live for a long time.