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How Do You Know When It’s a NET?

Doctors often have difficulty diagnosing a neuroendocrine tumor (NET) in its early stages. There are several reasons for this. Most of the symptoms are nonspecific, meaning they're similar to symptoms that can be caused by many things:

  • Flushing can also be a perimenopausal symptom, reaction to alcohol, or side effect of a drug

  • Diarrhea can also be a sign of a number of gastrointestinal (GI) tract diseases, such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and gastritis

  • Wheezing can be mistaken for asthma or other respiratory problems

Recognizing a pattern to the symptoms can be part of the process of considering the diagnosis of NETs. That’s why it’s important to tell your doctor about all of the symptoms you experience, even if they don’t seem to be related to the symptom that’s causing you concern.

Because it's a fairly rare condition, your doctor might not have been looking for a NET when your symptoms first started.

How Are NETs Diagnosed?

There are several tests that your doctor can use to diagnose a NET and to monitor it once it has been diagnosed. Diagnosis may start with testing for biochemical markers, followed by imaging tests to try and visualize the tumor.

Tests that can help confirm a NET diagnosis

Click each tab below to learn about how these tests are performed.

Biochemical tests

Biochemical tests measure the levels of certain substances in your blood or urine. Your doctor may order biochemical tests to help determine whether or not you actually have a NET or to measure the amount of certain hormones in your body.

5-Hydroxyindoleacetic acid test

A 5-hydroxyindoleacetic acid (5-HIAA) test is a 24-hour urine test. In certain circumstances, 5-HIAA testing can be useful for some patients with a functional GI NET.

Your doctor may order a 5-HIAA test to measure the amount of serotonin in your blood. Serotonin is a hormone mostly made by cells found in the GI tract (digestive system) that helps with various bodily functions, such as digestion. Your doctor may order this test more than once to help watch for a NET that may cause carcinoid syndrome.

How the test is performed

You will urinate into a container over a 24-hour period.

After 24 hours, you will return the container to be tested.

Please note that some types of foods and medicines can increase the level of 5-HIAA detected in your urine, which can cause misleading results. Ask your doctor for a complete list of foods and medicines that you should avoid before a 5-HIAA test.

Here are some foods that can increase the 5-HIAA detected in your urine:

  • Bananas

  • Avocados

  • Kiwis

  • Plums

  • Eggplants

  • Tomatoes

  • Plantains

  • Pineapples

  • Pecans

  • Walnuts

Medicines with:

  • Guaifenesin (found in cough medicine)

  • Acetaminophen

  • Salicylates (found in aspirin)

  • L-DOPA (found in Parkinson's disease medicine)

As well as:

  • Caffeine

  • Nicotine

Chromogranin A

The chromogranin A (CgA) blood test is a marker sometimes used to help detect and monitor the activity of some types of NETs. This includes functional tumors, which are the type that release (secrete) hormones.

A CgA test is a measure of your CgA level. However, increased levels of this marker may also be caused by other factors, such as renal failure, chronic atrophic gastritis, or the use of proton pump inhibitors. Because of these limitations, this test is less frequently used today than in the past.

You may continue to have this test so your doctor can measure your CgA levels over time.

How the test is performed

A needle is inserted into your arm, and a sample of blood is taken. The sample is sent to a laboratory to be tested. Measurements may vary with meal consumption, so patients may be required to fast before a CgA test. CgA tests may be performed every 3 to 6 months.

Imaging tests

Imaging tests use specialized machines to look at your organs and tissues. These tests may help with the diagnosis of NETs or to find out whether your tumor has grown or changed.

Computed tomography

CT scan showing the location and size of a carcinoid tumor

A computed tomography (CT) scan shows the location and size of your tumor. Over time, these scans may help your doctor determine if your tumor has grown, changed, or spread.

How the test is performed

A CT scanner is shaped like a large doughnut standing on its side. You will lie on a table that slides you into the doughnut hole while the scanner takes pictures. You may also hear clicking or whirring noises. You may need to hold your breath to ensure that the pictures are clear. If your doctor orders your test with "contrast," you will either drink a fluid or receive an intravenous (IV) injection before the test. Contrast helps certain areas show up in the images.

Magnetic resonance imaging

Patient receiving an MRI scan to examine a carcinoid tumor

A magnetic resonance imaging (MRI) scan shows the difference between healthy tissue and a tumor. Your being scanned over time will help your doctor tell if your tumor has grown, changed, or spread.

How the test is performed

During the test, you will lie on a table while the machine takes pictures. The machine may make clicking or beeping noises. You will need to stay very still to ensure the images are clear. If your doctor orders your test with "contrast," you will get an IV injection before the test. Contrast helps certain areas show up better in the images.

Markers in scans

Many NETs have been found to overexpress certain types of molecules called receptors on their surface. The abundance of these receptors on the surface of NETs has allowed the development of different markers that can recognize the receptors and bind to them, allowing tumors to be visualized using a positron emission tomography (PET) scan and other imaging techniques. These markers often work by including a radioactive “tag.”

Goals of Cancer Treatment

Management of a NET depends on several factors, including the stage of disease, size and location of the tumor, and whether or not you have any other serious medical conditions:

  • For the patient whose NET has not spread very far, surgery to remove the NET is generally the preferred treatment

  • For the patient whose NET has spread and cannot be removed, other treatments, such as chemotherapy or targeted therapies, may be considered

In addition, there are medical treatments that may be prescribed for the symptoms of a NET, such as with carcinoid syndrome. Your health care professional can discuss all of this information with you.

Ongoing Monitoring of a NET

Even if your NET has been surgically removed, your doctor may recommend periodic monitoring by regular biochemical tests, as well as computed tomography (CT) or magnetic resonance imaging (MRI) scans. This kind of testing can help determine if a tumor has returned, as well as track how a NET is responding to treatment.

Resources and Support

If you're looking for helpful resources on NETs and carcinoid syndrome, this is the place for you.