Lab and Imaging Tests for Neuroendocrine Tumors

Medically Reviewed by Brunilda Nazario, MD on March 04, 2019
5 min read

Neuroendocrine tumors (NETs) look and act differently than a lot of other tumors, which can make them harder to spot. Your doctor may ask you to take several different tests that can help them make a diagnosis.

"Many of the NETs are what we call low-grade tumors, which means they're very slow growing," says Bassel El-Rayes, MD, director of the gastrointestinal oncology program at the Emory University Winship Cancer Institute. Because of that, you may not notice any symptoms at first.

Sometimes doctors discover NETs accidentally, while doing tests to look for other diseases. But if you do have any symptoms, like diarrhea, fatigue, or redness and heat in your face, let your doctor know right away. Lab and imaging tests can find the cause -- and the right treatment.

To start, your doctor will do a physical exam and ask questions like:

  • What kind of symptoms have you had?
  • When did they start?
  • How often do you have them?

One way your doctor can check if you have NETs is to take advantage of the fact that some tumors release hormones and proteins. They can do tests that find these substances in your blood and urine.

Blood tests may find higher-than-normal levels of:

  • Gastrin
  • Glucagon
  • Insulin
  • Serotonin
  • Somatostatin
  • Vasoactive intestinal polypeptide

Another blood test checks for chromogranin A (CgA), a protein that NETs release. About 60% to 80% of NET tumors in the pancreas and digestive system raise CgA levels in the blood.

Your doctor can also test your urine for high levels of a substance called 5-HIAA, which comes from the breakdown of serotonin. For this test, you'll take a 24-hour urine sample, which means you collect all of your pee during one day and bring it to your doctor for testing.

While lab tests check for things your tumor releases, imaging tests let your doctor look inside your body and see the tumor. Which ones your doctor uses depends on your symptoms.

CT (computed tomography) uses a powerful X-ray to make detailed pictures inside your body. It can detect tumors and show if they've spread to distant organs, such as the liver.

MRI (magnetic resonance imaging) is another test that uses powerful magnets and radio waves to make pictures of organs and structures inside your body.

"CT scan and MRI give you an idea about the anatomy, like the location and size of the tumors," El-Rayes says.

For both of these tests, you lie down on a table that slides into the opening of a large, scanning machine. The technician will ask you to be still during the scan. You'll be able to talk to them through a speaker. During an MRI scan, you might hear loud noises that sound like tapping or banging. You can wear ear plugs or headphones if this bothers you.

Before either of these scans, your doctor may inject you with a special dye to see the inside of your body more clearly. You might not be allowed to have anything to eat or drink for a few hours beforehand.

While imaging tests show you where the tumor is and what it looks like, nuclear medicine tests go one step further. They give you an idea of how the tumor functions, El-Rayes says. Together these two types of tests give doctors "a complete picture."

You may get one of two kinds of nuclear medicine tests:

Octreotide scan (octreoscan). It helps your doctor find NETs anywhere in your body.

"Most NET cells possess a very specific lock that allows you to put a key in it to detect," says Thomas O'Dorisio, MD, director of neuroendocrine tumor clinics at the University of Iowa. That lock is called a somatostatin receptor.

A lab technician injects a small amount of an octreotide with a radioactive substance called a tracer into a vein in your arm or hand. The tracer attaches to tumor cells that have the somatostatin receptor on their surface.

Next, a special camera will find where the tracer has collected. You'll have scans 4, 24, and possibly 48 hours after you get the tracer.

"If the tumor has the receptor, it will light up on the scan," El-Rayes says.

PET, or positron emission tomography. It also makes pictures inside your body. Just like with an octreotide scan, a technician puts a little bit of something that's radioactive into one of your veins. Cancer cells pick up this substance, which makes them easier to see.

A PET scan creates a clearer image than an octreoscan. Another advantage: It takes less time -- only 2 hours -- says Lowell Anthony, MD, chief of the division of medical oncology at the University of Kentucky. "It's a lot more convenient for patients."

Your doctor removes some cells from the tumor. They may take it out with a needle that they put through your skin. A CT scan or other imaging test can help them find the right spot.

For your biopsy, your doctor may also look inside your digestive tract with a thin, flexible, lighted tube with a camera on the end called an endoscope. One type has an ultrasound on the tip -- a device that makes an image with sound waves.

You'll get medicine to relax you before the endoscopy. You may need to fast overnight before the procedure.

"We would like patients to be off medications that thin their blood, like aspirin, so they don't bleed during the biopsy," El-Rayes says.

After the cells are removed, a specialist checks them under a microscope to see if they're cancer. The biopsy also let them look at their features and predict how your disease may act next, El-Rayes says.

Your biopsy sample may also be tested to see if it contains certain genes or proteins. If it does, your doctor can suggest treatments that target those substances. 

If the results show you have a cancerous NET, your doctor will give your disease a grade and stage. These describe the size of your cancer, how it looks under a microscope, and whether it has grown and spread.

"Each of the tests is a piece of the puzzle. The pieces have to fit together nicely to make a complete picture," El-Rayes says. Your doctor will use all of the information gathered from your tests to find the best treatment for you.