Using a PET Scan for Cancer Staging and Treatment

A PET scan is also known as positron emission tomography. It uses a tracer with low levels of radiation to find places in your body where cells are unusually active—which can mean they're cancerous. A PET scan can show whether cancer has spread and to where.

PET scans provide insight that can help your medical team diagnose you and determine treatment options. Learn the benefits and the risks along with why these tests are recommended.

woman about to receive a nuclear imaging scan

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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 healthcare provider if you are pregnant or breastfeeding, have diabetes, or if you've had an allergic response to radioactive tracers in the past.

PET Scan for Cancer

Your healthcare provider may recommend a PET scan if cancer is suspected through other imaging tests, including:

Before recommending a PET scan, your healthcare provider 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 inconclusive 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 since the inflammation may be caused by something other than cancer.

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 that treatment it is working and to 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 an area with a lot of radioactive activity is malignant (cancerous) or benign (noncancerous). If your results are inconclusive, your healthcare provider will order further tests and care options.


PET scans can be used to determine how much cancer is in a person's body and how far the 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

  • Low level of radiation exposure (not harmful unless pregnant or breastfeeding)

  • Allergic reaction (extremely rare)

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 healthcare provider wants to examine.

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

If a nuclear test shows hot spots of potentially unhealthy tissue, other imaging tests can be used to gain more insight.

Computed Tomography (CT)

CT scans use an X-ray to take multi-angled pictures inside your body, which are then used to construct 3D 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 in detecting and diagnosing cancer in soft tissues. The combination test can provide a clearer picture of the location, spread, and growth of a tumor than either test by itself. 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 3D pictures of these areas are able to be examined.

Magnetic Resonance Imaging (MRI)

MRIs use magnets and radio waves to show slices of soft tissue, creating images that show where unhealthy tissue is located. An injection of contrast liquid may be given to show the tumors as a different, bright color in the images. MRI helps healthcare providers locate and possibly determine whether a tumor is cancerous or noncancerous.

Treatment Plan

After a PET scan is complete, a radiologist or healthcare provider trained in nuclear medicine will go over the results and send the information they find to your healthcare provider. PET scans help to guide treatment by providing information on where the cancer is located and how far it has spread, 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 that too. 

PET Scans Help Identify Recurrences of Cancer

Since PET scans can detect potential cancer sooner than other tests, they are 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 the use of 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 healthcare provider about any concerns you may have.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Cancer Institute. Positron emission tomography scan.

  2. National Cancer Institute. How cancer is diagnosed.

  3. Canadian Cancer Society. Positron emission tomography (PET) scan.

  4. Radiology Info. Positron emission tomography—computed tomography (PET/CT).

  5. American Cancer Society. Nuclear medicine scans for cancer.

By Rachel Macpherson
Rachel MacPherson is a health writer, certified personal trainer, and exercise nutrition coach based in Montreal.