PET Scan: Cancer Staging and Treatment


A PET (positron emission tomography) scan is a type of imaging test that uses radioactive glucose (radiotracer) to see where cancer cells may be. Since cancer cells intake more glucose than normal cells, injecting some glucose into a vein can reveal where cancerous cells are in the body when scanned and examined with computerized images.

With more insight, doctors can see where cancer cells are in the body, which helps them determine treatment options.

Cancer tests like PET scans can cause anxiety. Learning the benefits and the risks along with why these tests are recommended can help you make informed decisions and hopefully relieve some of your concerns.

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Who Should Not Have a PET Scan?

Although PET scans are safe, there are some conditions where they are not recommended. Be sure to tell your doctor if you are pregnant or breastfeeding, have diabetes, or if you’ve had an allergic response to radioactive tracers.

PET Scan for Cancer

Your doctor may recommend a PET scan if cancer is suspected. Other forms of visual tests that detect cancer include:

Before recommending a PET scan, your doctor may do a physical exam and ask about your family’s medical history. Additionally, lab tests of your blood, urine, or other bodily fluids may be ordered.

Since abnormal lab tests like these do not necessarily mean you have cancer, scans such as PET or other imaging techniques may be used.

Radiotracers concentrate in tumors or areas of the body that are inflamed and don’t always clearly show that this tissue is cancerous. However, PET scans reveal possible cancerous areas earlier than other forms of testing can, making them very valuable for early detection and treatment.

If a cancer diagnosis is given, PET scans may be recommended throughout treatment to see if it is working and assess the likely outcome of the disease.

After cancer treatment, PET scans can be used to check for cancer recurrence.


PET Scans can help diagnose new or recurrent cancer.

Cell growth can be detected with a PET scan, but not all cancer types can be seen. Further tests typically need to be performed to complete the diagnosis.

Additionally, other tests will be necessary to determine whether or not an area with a lot of radioactive activity is malignant (cancerous) or benign (non-cancerous). If your results are abnormal, your doctor will order further tests and care options.


PET scans can be used to determine how far cancer has spread, which is called staging. Since PET scans can detect more cancerous sites than CT scans alone, they are often used in the initial staging and follow-up testing to see if and how the cancer is spreading. PET scan results may lead to changes in your treatment plan.

The benefits of PET scans for cancer outweigh the potential risks


  • Early detection

  • Accurate diagnosis

  • Customized treatment plan

  • Detailed images not available with other tests

  • Less invasive and expensive than exploratory surgery

Other Tests

Other imaging tests, such as CT and MRI scans, are often done in combination with PET scans. CT scans and MRIs can provide more information on cancerous (malignant) tumors and lesions. Which test is used can depend on the organs the doctor wants to examine.

Nuclear scans, like PET, cannot always reveal whether a tumor is cancerous.

Other imaging tests can be used on the areas shown in nuclear imaging scans to gain more insight on an area pinpointed after a nuclear test shows hot spots of potential unhealthy tissue. 

Computed Tomography (CT)

CT scans use an x-ray to take multi-angled pictures inside your body, which are then used to construct 3-D images of your organs. Contrast liquid may be swallowed and/or injected before the test to show tumors more efficiently. 

CT/PET together in one scan is a more advanced scanning method that is especially helpful for detecting and diagnosing cancer in the soft tissues. The combination test can provide a clearer picture of the location, spread, and growth of a tumor than if either test is completed alone. Moreover, the combined scan is more convenient for patients since they only have to go through a single test, rather than two separately.

Combined Pet/CT Scanners Perform Almost All Pet Scans Today

Since PET and CT scans used together provide the best picture of cancerous tissue, they are used in almost all PET scans today. This way the areas where unhealthy tissue exists and the anatomical 3-D pictures of these areas are able to be examined.

Magnetic Resonance Imaging (MRI)

MRIs use magnets and radio waves to show slices of tissue, creating images that show healthy and unhealthy tissues. An injection of contrast liquid may be given to show the tumors as a different, bright color in the images. MRI helps determine whether a tumor is cancerous or non-cancerous.

Treatment Plan

After a PET scan is complete, a radiologist or doctor trained in nuclear medicine will go over the results and send the information they find to your doctor. PET scans help to guide treatment by providing information on how far cancer has spread (staging) as well as if a particular cancer treatment, such as chemotherapy, is working. If cancer returns or spreads to other parts of the body, PET scans can reveal this too. 

PET Scans Help Identify Recurrences of Cancer

Since PET scans can detect potential cancer sooner than other tests, it is often used during the follow-up stages after cancer has been treated to catch potential recurrences.

A Word From Verywell

Cancer testing and diagnosis can be a scary and emotional time. Being educated about the various aspects of this process, like PET scans can help relieve some of the anxiety. Be assured that, in general, nuclear imaging tests like PET scans are very safe and the benefits of getting the test outweigh the potential downsides. You can always talk to your health care provider about any concerns you may have.