Neuroendocrine Tumor of the Gastrointestinal Tract: Diagnosis

Approved by the Cancer.Net Editorial Board, 07/2022

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 neuroendocrine tumor of the gastrointestinal tract (GI tract NET). They also do tests to learn if cancer has spread to another part of the body from where it started. If the cancer has spread, it is called metastasis. 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.

How a GI tract NET is diagnosed

There are different tests used for diagnosing a GI tract NET. Not all tests described here 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 an imaging scan or a medical procedure done for reasons unrelated to the tumor. Imaging scans show pictures of the inside of the body. For example, many NETs of the appendix are found during surgery to remove the appendix, called an appendectomy. NETs in the stomach and duodenum, which is 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 affect the actions of certain cells or organs. The hormone serotonin, a neurotransmitter involved in behavior 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.

  • Biopsy. A biopsy is the only way to make a definite diagnosis, even if other tests can suggest that cancer is present. During biopsy, a small amount of tissue is removed for examination under a microscope and is normally required to make a diagnosis of NET. A pathologist 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.

  • Biomarker 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.

  • Endoscopy. An endoscopy shows the lining of the upper digestive system using a thin, lighted, flexible tube called an endoscope. The person may be sedated as the tube is inserted through the mouth, down the esophagus, 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.

  • 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 tumors. 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 lymph nodes located in the area behind the abdomen. 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 and/or given as a liquid to swallow.

  • Magnetic resonance imaging (MRI). An MRI produces detailed images of the inside of the body using magnetic fields, not x-rays. 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 and/or given as a 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. However, the amount of radiation in the tracer is too low to be harmful. PET-CT scans are the type of imaging used for NETs. There are 3 types of tracers used in a PET scan: gallium-68 (68Ga) DOTATATE, copper-64 (64Cu) DOTATATE, and (18F) fluorodeoxyglucose (FDG).

    • 68Ga DOTATATE PET and 64Cu DOTATATE PET are forms of somatostatin receptor imaging and are primarily used to look at slow-growing NETs (grades 1 and 2, see Stages and Grades). Somatostatin receptors are proteins present on the surface of a NET cell that serve as a target for these imaging agents. When the 68Ga or 64Cu attaches to the somatostatin receptor and a picture is taken, cancer spots glow like light bulbs.

    • 18F FDG PET scan is another type of PET scan, but it does not use the somatostatin receptor. It is sometimes used for faster-growing neuroendocrine carcinomas (grade 3 NECs).

After diagnostic tests are done, your doctor will review the results with you. If the diagnosis is a tumor, these results also help the doctor describe it. This is called staging.

The next section in this guide is Stages and Grades. It explains the system doctors use to describe the extent of the disease. Use the menu to choose a different section to read in this guide.