Lab and Imaging Tests for Neuroendocrine Tumors

Medically Reviewed by Michael Dansinger, MD on May 24, 2022
4 min read

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

Many of these tumors grow very slowly. 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 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 whether you have a NET 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 and urine tests may find higher-than-normal levels of these chemicals, or substances that are made when they break down:

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

Another blood test checks for chromogranin A (CgA), a protein that NETs release. About 60%-80% of NET tumors in the pancreas and digestive system raise CgA levels in your 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 need a 24-hour urine sample. That 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. This way, they can learn more about its location and size. Which tests your doctor uses depends on your symptoms.

CT (computed tomography) uses a powerful X-ray to make detailed pictures inside your body. It can find tumors and show if they've spread to other organs, like your 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.

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 the technician through a speaker. During an MRI scan, you might hear loud noises that sound like tapping or banging. You can wear earplugs or headphones if this bothers you.

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

While imaging tests show your doctor where the tumor is and what it looks like, nuclear medicine tests go a step further. They can give your doctor an idea of how the tumor functions. 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. It works because most NETs contain certain proteins called somatostatin receptors.

A lab technician injects a small amount of 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 surfaces.

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 a tumor has the receptor, it will show up on the scan.

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.  

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. This is 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. And you'll need to avoid medications that can thin your blood, like aspirin.

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

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. This information will help your doctor decide on the best treatment for you.