Gastrointestinal Tract Neuroendocrine Tumors
The most common places in the body where NETs form is the gastrointestinal tract (GI tract) or digestive system. The GI tract starts at the oesophagus and ends at the anus, and it plays a central role in digesting food and liquid and in processing waste.
Here is a general overview of where GI tract NETs start:
- 39% occur in the small intestine
- 15% occur in the rectum
- 7% occur in the appendix
- 5% to 7% occur in the colon
- 2% to 4% occur in the stomach
Symptoms of a GI tract NET
The most common places in the body where NETs form is the GI tract or digestive system. The GI tract starts at the oesophagus and ends at the anus, and it plays a central role in digesting food and liquid and in processing waste.
GI tract NETs may cause tumor-related symptoms. GI tract NETs are also the type of NET most likely to cause carcinoid syndrome (see below), which has its own set of symptoms.
People with a GI tract NET may experience the following tumor-related symptoms or signs:
- Abdominal pain caused by blockage of the intestines
- Diarrhoea, especially in people who have carcinoid syndrome, had part of their intestines removed, or had their gallbladder removed.
- Bright, red blood in the stool or dark, tarry stool. This is a sign of intestinal bleeding.
- Scale-like skin sores, which can be a sign of pellagra, a severe deficiency of vitamin B3
- Mental disturbances, another sign of pellagra
- Nausea and vomiting
Neuroendocrine Tumor of the Gastrointestinal Tract: Diagnosis
Approved by the Cancer.Net Editorial Board, 10/2019
ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find the cause of the medical problem. Use the menu to see other pages.
Doctors use many tests to find, or diagnose, a GI tract NET. They also do tests to learn if cancer has spread to another part of the body from where it started. If this happens, it is called metastasis. For example, imaging tests can show if the cancer has spread. Imaging tests show pictures of the inside of the body. Doctors may also do tests to learn which treatments could work best.
For most types of cancer, a biopsy is the only sure way for the doctor to know if an area of the body has a tumor. In a biopsy, the doctor takes a small sample of tissue for testing in a laboratory. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis.
This section describes options for diagnosing a GI tract NET. Not all tests listed below will be used for every person. Your doctor may consider these factors when choosing a diagnostic test:
- The type of cancer suspected
- Your signs and symptoms
- Your age and general health
- The results of earlier medical tests
Most GI tract NETs are found unexpectedly when people have x-rays or a medical procedure done for reasons unrelated to the tumor. For example, many NETs of the appendix are found during surgery to remove the appendix, called an appendectomy. NETs in the stomach and duodenum, the top of the small intestine, are usually found during an endoscopy (see below).
If a doctor suspects a GI tract NET, they will ask for a complete medical and family history and perform a thorough physical examination. In addition, the following tests may be used to diagnose a GI tract NET:
- Blood/urine tests. The doctor may need samples of your blood and urine to check for abnormal levels of hormones and other substances. A hormone is a substance that can cause symptoms. The hormone serotonin, a neurotransmitter involved in behaviour and depression, is made by some NETs. Some blood tests check for tumor markers, which are proteins that can indicate whether or not a tumor is growing. Chromogranin A is a commonly measured tumor marker for NETs, but its measurement alone is not enough to make the diagnosis and it cannot be used alone to check whether a NET has come back, called a recurrence, or begun to grow or spread, called progression.
- A biopsy is the removal of a small amount of tissue for examination under a microscope and is normally required to make a diagnosis of NET. A pathologist then analyzes the sample(s) removed during the biopsy. A pathologist is a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease.
- Molecular testing of the tumor. Your doctor may recommend running laboratory tests on a tumor sample to identify specific genes, proteins, and other factors unique to the tumor. Results of these tests can help determine your treatment options. This testing is less helpful in NETs than in other cancers.
- An endoscopy allows the doctor to see the lining of the upper digestive system with a thin, lighted, flexible tube called an endoscope. The person may be sedated as the tube is inserted through the mouth, down the oesophagus, and into the stomach and small bowel. Sedation is giving medication to become more relaxed, calm, or sleepy. If an abnormality is found, a biopsy will be performed.
A colonoscopy is a type of endoscope that is inserted through the anus and into the colon. It can be used to diagnose a tumor in the lower section of the digestive tract.
- Endoscopic ultrasound. An ultrasound uses sound waves to create a picture of internal organs. This procedure is often done at the same time as an upper endoscopy. During an endoscopic ultrasound, a machine that produces the sound waves, called a transducer, is inserted into the upper digestive tract through the mouth. The endoscopic ultrasound can show enlarged lymph nodes, which may help the doctor find a tumor or figure out the stage of the disease.
- X-ray. An x-ray is a way to create a picture of the structures inside the body. Sometimes, a GI tract NET may not show up on an x-ray because of its size or location, so the doctor may also recommend other types of scans.
- Barium x-rays.During a barium swallow, a person swallows a liquid containing barium that coats the lining of the oesophagus, stomach, and intestines. Then a series of x-rays are taken. The barium makes abnormalities easier to see on the x-ray. If there is an abnormality, an endoscopic biopsy can help make a diagnosis of cancer.
A barium enema may be given before x-rays are taken to show the inner surface of the large intestine. During this test, a barium solution is given through the anus and flows throughout the colon. Then the x-rays are taken.
- Computed tomography (CT or CAT) scan. A CT scan takes pictures of the inside of the body using x-rays taken from different angles. A computer combines these pictures into a detailed, 3-dimensional image that shows any abnormalities or tumor. A CT scan can be used to measure the tumor’s size. Additionally, a CT scan is used to see if a tumor has spread to the liver and to find a NET in the retroperitoneal (the area behind the abdomen) lymph nodes. Sometimes, a special dye called a contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a patient’s vein or given as a pill or liquid to swallow.
- Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. MRI can be used to measure the tumor’s size. A special dye called a contrast medium is given before the scan to create a clearer picture. This dye can be injected into a patient’s vein or given as a pill or liquid to swallow.
- Nuclear medicine imaging. During this test, a small amount of a radioactive drug, called a tracer, is injected into a patient’s vein. The body is then scanned to show where the radioactivity has built up in the body. There are a few available methods of nuclear medicine imaging in NETs, including 2 types of PET-CT scans.
- Positron emission tomography (PET) or PET-CT scan. A PET scan is usually combined with a CT scan (see above), called a PET or PET-CT scan. The 2 types of tracers used in a PET scan include gallium-68 (68Ga) DOTATATE and (18F) fluorodeoxyglucose (FDG). The 68Ga DOTATATE PET is the primary scan used to look at slow-growing NETs (grades 1 and 2, see Stages and Grades). An FDG PET scan is sometimes used for faster-growing NETs (grade 3). The 68Ga DOTATATE PET scan has replaced a different method of nuclear imaging called OctreoScan because it is more effective.
After diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is cancer, these results also help the doctor describe the tumor. This is called staging.