Neuroendocrine Tumors: Diagnosis

Approved by the Cancer.Net Editorial Board, 01/2021

ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find the cause of a medical problem. Use the menu to see other pages.

Doctors use many tests to find, or diagnose, a 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 tumors, 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 NET is diagnosed

There are many tests used for diagnosing a 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 NET suspected

  • Your signs and symptoms

  • Your age and general health

  • The results of earlier medical tests

Most NETs are found unexpectedly when people have x-rays or a medical procedure done for reasons unrelated to the tumor. If a doctor suspects a 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 NET:

  • Biopsy. biopsy is the removal of a small amount of tissue for examination under a microscope and is 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. It should be noted that a tumor suspected to be a pheochromocytoma should not be biopsied, unless it is absolutely necessary to confirm a diagnosis. A biopsy of these tumors can be life-threatening. See the Pheochromocytoma and Paraganglioma section for more information on these tumors.

  • Blood/urine tests. The doctor may need samples of your blood and urine to check for abnormal levels of hormones and other substances. Urine tests check the amount of 5-HIAA, a breakdown product of serotonin which is made by some NETs. Measurements of blood serotonin levels may also be taken; however, these are less reliable due to fluctuations. A blood test to measure chromogranin A, a protein produced by tumor cells, is also sometimes performed after diagnosis to watch the tumor’s response to treatment. Chromogranin A is a tumor marker and not a hormone; it is not part of diagnostic testing.

  • Biomarker testing of the tumor. Your doctor may recommend running laboratory tests on a tumor to identify specific genes, proteins, and other factors unique to the tumor. This may also be called molecular testing of the tumor. Results of these tests can sometimes help determine your treatment options. This testing is less helpful in NETs than in other cancers.

  • Endoscopy. An endoscopy allows the doctor to see inside the body with a thin, lighted, flexible tube called an endoscope. There are many different types of endoscopy, including upper endoscopy to examine the esophagus and stomach and colonoscopy to examine the rectum and colon. The person may be sedated as the tube is gently inserted into the body. Sedation is giving medication to become more relaxed, calm, or sleepy. If an abnormality is found, a biopsy will be performed (see above).

  • Ultrasound. An ultrasound sound waves to create a picture of the internal organs. Tumors generate different echoes of the sound waves than normal tissue. This means that when the waves are bounced back to a computer, creating images, the doctor can locate a mass inside the body. There are different types of ultrasounds used to examine different parts of the body. In some cases, a biopsy may be done during the procedure.

  • X-ray. An x-ray is a way to create a picture of the structures inside the body using a small amount of radiation. Sometimes, a 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. If the doctor suspects a GI tract NET, a barium x-ray may be done. A person swallows a liquid containing barium that coats the lining of the esophagus, stomach, and intestines. Then a series of x-rays is 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 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. 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. However, the amount of radiation in the substance is too low to be harmful. PET-CT scans are the type of imaging used for NETs. A PET scan is usually combined with a CT scan (see above), called a PET or PET-CT scan. 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 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. The 68Ga DOTATATE PET scan has replaced a different method of nuclear imaging called OctreoScan because it is more effective. A 64Cu DOTATATE PET scan is the latest tracer to be made available to locate NETs.

    • 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 NETs (grade 3).

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

The next section in this guide is Stages. 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.