PET scan

A woman inside a PET scan machine

Positron Emission Tomography, also known as a PET scan, is an imaging test used to detect cancer throughout the body.

PET scans use a radioactive tracer that helps doctors (radiologists or nuclear medicine specialists) find areas in the body where cancer may have traveled. Radioactive tracers, or radiotracers, release a very small amount of radiation, which is what makes the images on the PET scanner.

A PET scan can show areas that other imaging tests, such as magnetic resonance imaging (MRI) or CAT or CT scan, may not show. On a PET scan, these areas show up brighter than other areas.

While PET scans are not used to screen for breast cancer, they can give doctors more information after a diagnosis is confirmed, such as whether cancer has traveled far from where it started. The test results can help you and your healthcare team make decisions about treatment.

There are different types of PET scans that use different radiotracers and have different purposes. On this page, we’ll talk about two types:

  • FDG (fluorodeoxyglucose) PET scans: These PET scans help identify areas of cancer in the body, provide information on whether a previous cancer has come back, and provide information on whether cancer treatment is working. FDG PET scans can be helpful for disease detection.
  • FES (fluoroestradiol) PET scans: These PET scans work to detect the presence of estrogen receptor-positive breast cancer cells in the body. FES PET scans can be helpful for determining whether sites of cancer have estrogen receptors and for making treatment decisions.

We’ll also walk you through what it’s like to get a PET scan, small risks, and paying for PET scans.


FDG PET scans

PET scans can be distinguished from one another in a few ways, including the type of radioactive tracer they use. The most commonly used PET scan tracer is fluorodeoxyglucose, or FDG, a radioactive sugar. The tracer is injected into the body and is taken up by cancer cells, enabling areas of cancer to show up on PET scan images. You may hear doctors using the term “FDG PET” to describe these scans.

After a breast cancer diagnosis, doctors may order an FDG PET scan to see if the cancer has traveled outside the breast to other areas in the body, such as distant lymph nodes or the bones, liver, lungs, or brain. Breast cancer that spreads to another part of the body is called metastatic breast cancer (MBC).

FDG PET scans can also be used to confirm:

FDG PET scans are very effective for detecting metastases in the body. A PET scan is often performed along with a CT scan, called a PET-CT, to more precisely locate areas of cells that may be cancerous.

Paying for FDG PET scans

Public health insurance, such as Medicare and Medicaid, covers the cost of FDG PET scans for people diagnosed with breast cancer. Many private health insurance companies require pre-authorization for certain tests, including PET scans. You may want to talk with your insurance provider if you and your care team are considering this test.


FES PET scans

A different radioactive tracer called fluoroestradiol (FES) (brand name: Cerianna) is also approved to be used with PET scans. This tracer detects estrogen receptor-positive lesions in people diagnosed with recurrent or metastatic estrogen receptor-positive breast cancer.

If you have been diagnosed with recurrent or metastatic breast cancer after being treated for an earlier breast cancer diagnosis, it’s important to know that characteristics about the breast cancer, including estrogen receptor status, can change. Biopsy and, in some cases, FES PET imaging can help confirm whether estrogen receptor status has changed. This helps you and your healthcare team decide on the most precise treatment for your diagnosis.

FES behaves like estrogen. When FES is injected into the body, it works to locate, attach to, and identify breast cancer cells that have estrogen receptors.

FES is used with PET scans to:

  • Provide more information on whether recurrent or metastatic breast cancer diagnosed with a biopsy is estrogen receptor-positive; this can be helpful if biopsy tissue test results were unclear
  • Get more information about estrogen receptor status in areas of breast cancer that are hard to biopsy, such as brain metastases or certain areas of bone metastases
  • Confirm estrogen receptor-positive metastatic disease in cancers that may be difficult to detect, such as invasive lobular breast cancer
  • Determine if all sites of disease are estrogen receptor-positive, which helps you and your doctors decide on the right treatment for you

Like PET scans that use FDG, PET scans that use FES do not replace biopsy for breast cancer diagnosis. However, if an area of breast cancer is too difficult to biopsy, FES PET scans can be used in the absence of a biopsy. They can also help doctors detect estrogen receptor status when other tests don’t give enough information to do so.

FES PET scans are not used to detect other receptors, such as human epidermal growth factor receptor 2 (HER2) or progesterone receptors (PR).

The National Comprehensive Cancer Network (NCCN), a group that provides recommendations for diagnosing and treating cancer, recommends FES PET scans in certain cases for people with recurrent breast cancer or MBC to help doctors with:

The American College of Radiology (ACR) imaging guidelines also recommend FES PET scans as an addition to biopsy for detecting estrogen receptor-positive areas of recurrent breast cancer or MBC.

FES PET scan effectiveness

When compared with the accuracy of biopsied breast cancer that has been tested for estrogen receptor status:

  • FES PET scans have been shown to accurately identify estrogen receptor-positive breast cancer 95% of the time
  • FES PET scans have been shown to predict estrogen receptor-negative breast cancer 80% of the time

If you are taking the endocrine therapies tamoxifen, elacestrant (Orserdu), or fulvestrant (Faslodex), a washout period (time not taking the medicine) is recommended before an FES PET scan. These medicines work by attaching to estrogen receptors. FES works the same way, so if you are taking one of these medicines, it’s harder for FES to attach to estrogen receptors to show estrogen receptor-positive breast cancer cells on the PET scan.

If you and your healthcare team are considering an FES PET scan for you, it’s best to get one before starting any of these medicines. If that’s not safe or possible for your situation, this kind of scan may not be right for you. FES PET can be performed in people taking other medicines, such as aromatase inhibitors, targeted therapies including CDK 4/6 inhibitors and mTOR inhibitors, and chemotherapy.

FES PET scan availability and insurance coverage

FES PET scans are not yet widely available in the United States. If you’ve been diagnosed with recurrent breast cancer or MBC, ask your doctor if this test is available in your area and, if so, whether it might be helpful in your treatment planning.

FES PET scans may be covered by health insurance companies, especially if they are used to help make treatment decisions. If your doctor recommends this test for you but your insurance company denies coverage, talk with your care team about options.

In addition, GE HealthCare, the maker of FES PET, has a Support Center offering guidance about how insurance can cover this test. You can call 833-946-6392 Monday through Friday, 8 a.m. to 6 p.m. ET to learn more.  

You can also visit our Financial matters section for information on covering the costs of breast cancer.

A woman lies on a bed before entering a PET scan machine, while three doctors speak with her

Getting a PET scan

PET scans, including FDG and FES PET scans, are usually done at an imaging center or hospital.

Before the test, a technologist will place an intravenous (IV) line into your vein and inject the radioactive tracer into the IV line.

If the scan is an FDG PET scan, your doctor will ask you not to eat or drink for several hours before the test. If you have diabetes or other illnesses, you will receive special instructions to ensure the test gives accurate results. Let your doctor know if you have food or drug allergies, too.

You will be asked to remove metal jewelry and other objects before the test. You may also be asked to change into a hospital gown.

After the tracer injection, you will sit quietly for about an hour while your body absorbs the material.

Then, you will lie on a narrow table that will move through a hole in the center of a round scanner. The PET scan machine looks somewhat like a CAT or CT scan machine or an MRI machine. During the scan, which lasts about 30 minutes, you’ll be reminded to lie very still so scanner can take pictures of your body.

Except for the needle prick from the tracer injection, you should not feel pain during the scan itself. The entire procedure takes about one to three hours.

PET scan results can be ready in as soon as 24 hours.


PET scan risks

Both FDG and FES PET scans expose people to a small amount of radiation that has not been shown to cause harm in the person being scanned. It’s important, though, to let your doctor know if you could be pregnant, because radiation contact can harm an unborn baby.

Also let your doctor know if you are breastfeeding. If you are breastfeeding, your doctor will give you specific instructions about how long to pause breastfeeding and what do with milk pumped shortly after the scan, so that your baby is not exposed to radiation from the radiotracer.


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Reviewed and updated: May 3, 2024

Reviewed by: Sophia R. O'Brien, MD


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