PET scans, short for positron emission tomography, can detect areas of cancer by taking images of the body’s cells as they work. First, you are injected with a substance made up of sugar and a small amount of radioactive tracer material. Cancer cells tend to be more active than normal cells, and they absorb more of the radioactive sugar tracer as a result. A special camera then scans the body to pick up any areas that are highlighted by the radioactive tracer and displays them on a computer screen. This helps radiologists identify areas where cells are suspiciously active, which can indicate cancer.
18F-fluorodeoxyglucose-positron emission tomography/computed tomography uses the tracer fluorine-18 fluorodeoxyglucose to highlight overactive cells, and scans the body with X-ray computed tomography, also called a CT or CAT scan. This type of PET scan is called FDG-PET/CT for short.
A study suggests that FDG-PET/CT can accurately diagnose breast cancer recurrence and is more accurate than contrast-enhanced CT scans and bone scintigraphy.
The study was published online on March 21, 2016 by the Journal of Clinical Oncology. Read the abstract of “[18-F] Fluorodeoxyglucose (FDG)-Positron Emission Tomography (PET)/Computed Tomography (CT) in Suspected Recurrent Breast Cancer: A Prospective Comparative Study of Duel-Time-Point FDG-PET/CT, Contrast-Enhanced CT, and Bone Scintigraphy.”
Right now, treatment guidelines don’t recommend any imaging tests other than mammography after primary treatment for breast cancer, and there are no clear recommendations about which imaging test is best for detecting breast cancer recurrence.
A CT scan uses a machine to take X-rays of the body from many different angles. A computer puts these images together to create detailed pictures of the area that is scanned. Contrast-enhanced CT means that you have a contrast dye solution injected into your arm before the scan starts. The contrast agent helps doctors see the differences between the various tissues and organs in your body.
Bone scintigraphy, also called a bone scan, is an imaging test that helps doctors determine if breast cancer has traveled to the bones. When you have a bone scan, you’re first injected with radioactive tracer material. This material is taken up by the body’s bone-making cells. Bone-making cells are found mostly in areas damaged by disease. A special camera then scans the body to pick up any areas that are highlighted by the radioactive tracer and displays it on a computer screen.
In this Danish study, 100 women whom doctors suspected had a breast cancer recurrence had all three tests: a FDG-PET/CT scan, a contrast-enhanced CT scan, and a bone scan. Eighty-three of the women were originally diagnosed with early-stage disease. The researchers didn’t know the stage of the cancer of the other 17 women.
The scans were read by two nuclear medicine specialists and four radiologists.
To assess the accuracy of the imaging tests, the researchers compared the imaging results to results of biopsies done to verify any recurrence.
The biopsies found that:
- 22 of the women had distant recurrence (breast cancer coming back in a part of the body away from the breast, such as the bones or liver):
- five of the women had only one site of distant metastasis
- eight women had two sites
- nine women had three or more sites
- 18 of the women had bone metastases
- 19 women had local recurrence only (breast cancer coming back in the same area where it was originally diagnosed)
- 59 women had no recurrence
When the researchers compared the results of the imaging tests to the biopsy results, they found that the FDG-PET/CT scans were more sensitive in diagnosing distant and local recurrences than the other two imaging techniques, no matter if the CT and bone scans were used alone or combined.
The FDG-PET/CT scans resulted in no false negatives and fewer false positives than the CT scans or the bone scans.
A false negative is when test results suggest that there is no cancer present when it really is there.
A false positive is when test results show an abnormal area that looks like a cancer but turns out to be normal. Ultimately the news is good: no cancer. But the suspicious area usually requires follow-up, extra tests, and extra procedures.
False positive rates were:
- Seven for FDG-PET/CT
- 18 for contrast-enhanced CT
- 10 for bone scintigraphy
"FDG-PET/CT did very well and also better than conventional imaging -- contrast enhanced CT and bone scintigraphy -- in diagnosing breast cancer recurrence," Malene Grubbe Hildebrandt, M.D., of the Odense University Hospital and corresponding author of the study, said in an interview. "Our study has been performed in a single institution with experience in performing PET since 2006, and we should be cautious when generalizing from our results. I think that a synthesis of literature, preferably based on more prospective studies in this field, is needed along with health economic assessments before more generalizing conclusions should be drawn.
"I would like to make a point of considering the patients' perspective and the economic consequences of implementing FDG-PET/CT in this patient group," she added. "We will continue doing analyses of the patients' perspective of having only one as compared to two diagnostic tests performed, and also of organizational and economic consequences of implementing FDG-PET/CT in this setting."
While these results are very encouraging, FDG-PET/CT isn’t use routinely to evaluate possible breast cancer recurrence. It’s an expensive, sophisticated test that requires special expertise, and it’s not available at all cancer centers. But as these results suggest, FDG-PET/CT may be able to diagnose breast cancer recurrence better than other standard imaging tests.
Although FDG-PET/CT is still being studied, if your doctor suspects that breast cancer has come back, you may want to ask about this study and if a FDG-PET/CT scan would be appropriate for your unique situation and if it’s available in your area.
For more information on tests used to detect breast cancer recurrence, visit the Breastcancer.org Screening and Testing pages.