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

The gastrointestinal (GI) tract is part of the body's digestive system, a series of hollow, muscular organs joined in a long, twisting tube from the mouth to the anus. The digestive tract processes nutrients in foods that are eaten and helps pass waste material out of the body:

• Food moves from the throat to the stomach through a tube called the esophagus.
• After food enters the stomach, it is broken down by stomach muscles that mix the food and liquid with digestive juices.
• After leaving the stomach, partly digested food passes into the small intestine and then into the large intestine.
• The end of the large intestine, called the rectum, stores the waste from the digested food until it is pushed out of the anus during a bowel movement.

Gastrointestinal (GI) neuroendocrine tumors (also called gastrointestinal carcinoid tumors) form from a certain type of neuroendocrine cell (a type of cell that is like a nerve cell and a hormone-making cell). These cells are scattered throughout the chest and abdomen but most are found in the GI tract. Neuroendocrine cells make hormones that help control digestive juices and the muscles used in moving food through the stomach and intestines. A GI neuroendocrine tumor may also make hormones and release them into the body.

GI neuroendocrine tumors are rare and most grow very slowly. Most of them occur in the small intestine, rectum, and appendix. Sometimes more than one tumor will form.

See the following for information about other types of neuroendocrine tumors:

• Pancreatic Neuroendocrine Tumors (Islet Cell Tumors) Treatment
• Childhood Gastrointestinal Neuroendocrine Tumors Treatment

Health history can affect the risk of GI neuroendocrine tumors.

Anything that increases a person's chance of getting a disease is called a risk factor. Not every person with one or more of these risk factors will develop GI neuroendocrine tumors, and they can develop in people who don't have any known risk factors. Talk to your doctor if you think you may be at risk.

Risk factors for GI neuroendocrine tumors include the following:

• Having a family history of multiple endocrine neoplasia type 1 (MEN1) syndrome or neurofibromatosis type 1 (NF1) syndrome.
• Having certain conditions that affect the stomach's ability to make stomach acid, such as atrophic gastritis, pernicious anemia, or Zollinger-Ellison syndrome.

Some GI neuroendocrine tumors have no signs or symptoms in the early stages.

Signs and symptoms may be caused by the growth of the tumor and/or the hormones the tumor makes. Some tumors, especially tumors of the stomach or appendix, may not cause signs or symptoms. Neuroendocrine tumors are often found during tests or treatments for other conditions.

Neuroendocrine tumors in the small intestine (duodenum, jejunum, and ileum), colon, and rectum sometimes cause signs or symptoms as they grow or because of the hormones they make. Other conditions may cause the same signs or symptoms. Check with your doctor if you have any of the following:

Duodenum

Signs and symptoms of GI neuroendocrine tumors in the duodenum (first part of the small intestine, that connects to the stomach) may include the following:

• Abdominal pain.
• Constipation.
• Diarrhea.
• Change in stool color.
• Nausea.
• Vomiting.
• Jaundice (yellowing of the skin and whites of the eyes).
• Heartburn.

Jejunum and ileum

Signs and symptoms of GI neuroendocrine tumors in the jejunum (middle part of the small intestine) and ileum (last part of the small intestine, that connects to the colon) may include the following:

• Abdominal pain.
• Weight loss for no known reason.
• Feeling very tired.
• Feeling bloated
• Diarrhea.
• Nausea.
• Vomiting.

Colon

Signs and symptoms of GI neuroendocrine tumors in the colon may include the following:

• Abdominal pain.
• Weight loss for no known reason.

Rectum

Signs and symptoms of GI neuroendocrine tumors in the rectum may include the following:

• Blood in the stool.
• Pain in the rectum.
• Constipation.

Carcinoid syndrome may occur if the tumor spreads to the liver or other parts of the body.

The hormones made by GI neuroendocrine tumors are usually destroyed by liver enzymes in the blood. If the tumor has spread to the liver and the liver enzymes cannot destroy the extra hormones made by the tumor, high amounts of these hormones may remain in the body and cause carcinoid syndrome. This can also happen if tumor cells enter the blood. Signs and symptoms of carcinoid syndrome include the following:

• Redness or a feeling of warmth in the face and neck.
• Abdominal pain.
• Feeling bloated.
• Diarrhea.
• Wheezing or other trouble breathing.
• Fast heartbeat.

These signs and symptoms may be caused by GI neuroendocrine tumors or by other conditions. Talk to your doctor if you have any of these signs or symptoms.

Imaging studies and tests that examine the blood and urine are used to diagnose GI neuroendocrine tumors.

In addition to asking about your personal and family health history and doing a physical exam, your doctor may perform the following tests and procedures:

• 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. The blood sample is checked to see if it contains a hormone produced by neuroendocrine tumors. This test is used to help diagnose carcinoid syndrome.
• Tumor marker test: A procedure in which a sample of blood, urine, or tissue is checked to measure the amounts of certain substances, such as chromogranin A, made by organs, tissues, or tumor cells in the body. Chromogranin A is a tumor marker. It has been linked to neuroendocrine tumors when found in increased levels in the body.
• Twenty-four-hour urine test: A test in which urine is collected for 24 hours to measure the amounts of certain substances, such as 5-HIAA or serotonin (hormone). An unusual (higher or lower than normal) amount of a substance can be a sign of disease in the organ or tissue that makes it. This test is used to help diagnose carcinoid syndrome.
• MIBG scan: A procedure used to find neuroendocrine tumors. A very small amount of radioactive material called MIBG (metaiodobenzylguanidine) is injected into a vein and travels through the bloodstream. Neuroendocrine tumors take up the radioactive material and are detected by a device that measures radiation.
• CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.
• MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body. This procedure is also called nuclear magnetic resonance imaging
• PET scan (positron emission tomography scan): A procedure to find malignant tumor cells in the body. A small amount of radioactive glucose (sugar) is injected into a vein. The PET scanner rotates around the body and makes a picture of where glucose is being used in the body. Malignant tumor cells show up brighter in the picture because they are more active and take up more glucose than normal cells.
• Endoscopic ultrasound (EUS): A procedure in which an endoscope is inserted into the body, usually through the mouth or rectum. An endoscope is a thin, tube-like instrument with a light and a lens for viewing. A probe at the end of the endoscope is used to bounce high-energy sound waves (ultrasound) off internal tissues or organs, such as the stomach, small intestine, colon, or rectum, and make echoes. The echoes form a picture of body tissues called a sonogram. This procedure is also called endosonography.
• Upper endoscopy: A procedure to look at organs and tissues inside the body to check for abnormal areas. An endoscope is inserted through the mouth and passed through the esophagus into the stomach. Sometimes the endoscope also is passed from the stomach into the small intestine. An endoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove tissue or lymph node samples, which are checked under a microscope for signs of disease.
• Colonoscopy: A procedure to look inside the rectum and colon for polyps, abnormal areas, or cancer. A colonoscope is inserted through the rectum into the colon. A colonoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer.
• Capsule endoscopy: A procedure used to see all of the small intestine. The patient swallows a capsule that contains a tiny camera. As the capsule moves through the gastrointestinal tract, the camera takes pictures and sends them to a receiver worn on the outside of the body.
• Biopsy: The removal of cells or tissues so they can be viewed under a microscope to check for signs of cancer. Tissue samples may be taken during endoscopy and colonoscopy.

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

The prognosis and treatment options depend on the following:

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