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Researchers Say PEM Scan May Be More Accurate Than MRI
WebMD Health News
Reviewed By Louise Chang, MD
The method, called positron emission mammography, or PEM, is also at least as accurate, if not more accurate, than breast MRI at finding true cancers, says Kathy Schilling, MD, director of breast imaging and intervention at the Center for Breast Care at Boca Raton Community Hospital in Florida.
Women undergo breast MRI when standard mammography results are hard to read, typically due to very dense breast tissue. But breast MRI is also associated with a high rate of false-positive test results that indicate cancer is present when it is not. Researchers believe that's due in part to hormonal changes that occur during a woman's menstrual cycle.
PEM is not affected by either breast density or a woman's hormonal status, Schilling tells WebMD.
That means "fewer women will be called back for additional tests and biopsies, which is emotionally traumatic for the patient as well as the family," she says.
Schilling presented results of a new study of PEM at the annual meeting of the Radiological Society of North America (RSNA).
Breast-Specific PET Scan
PEM can be thought of as breast-specific positron emission tomography, or PET, says RSNA spokeswoman Stamatia Destounis, MD, of Elizabeth Wende Breast Care in Rochester, N.Y.
It involves injecting the body with a small amount of radioactive tracer dye that is bound to sugar. Fast-growing cancer cells feed on the sugar and utilize it more quickly than normal cells, so they appear brighter on images created by the PET scanner.
PEM isn't meant to replace mammograms or breast MRI, but rather act as an extra tool, Destounis tells WebMD. "It may fulfill a need when mammograms and MRI don't give us all the information we need."
But PEM correctly detected 90% of early, noninvasive cancers known as ductal carcinoma in situ (DCIS) confined to the ducts of the breast, while MRI was only accurate in 83% of cases. And PEM spotted 100% of early, tiny, invasive tumors less than 5 millimeters in diameter, while MRI found them only 75% of time.
PEM gave false-positive results to 18% of women who didn't have tumors. The comparable figure for MRI testing was 33%.
All the findings could have been due to chance. But Schilling thinks that they will take on what researchers call statistical significance -- meaning there's less than five-in-100 odds that they're due to chance -- as more women are studied.
PEM Accurate in Women With Dense Breasts
The researchers also looked at PEM alone to see if was affected by breast density or hormonal status. It wasn't, successfully detecting cancer in 77% of women with extremely dense breasts and in 88% of women with dense breasts. As for premenopausal women -- whose hormonal fluctuations during the menstrual cycle can influence MRI results -- PEM proved accurate in 88% of cases.
"Unless breast MRI is performed on days seven through 14 of the menstrual cycle, reading images is extremely difficult," Schilling says. With PEM, we don't have that problem."
Another advantage of PEM is that it avoids the close confinement of an MRI exam, during which a woman's arms are restrained and "she has to go into the bore of the magnet," Schilling says. During PEM, a woman sits upright and has freedom to move around a bit, she says.
Doctors also find it easier, as breast MRI exams produce more than 2,000 images to be interpreted, while PEM produces just 48 images that can be correlated with a woman's mammogram, she says.
Schilling notes that PEM is already approved for use in some women who have breast cancer, to see if their cancer has spread or if their treatment is working. If the findings of the new study can be replicated in larger trials "it will be a new item in our toolbox for screening high-risk women for cancer," she says.
One such study, of 400 women, is under way.
SOURCES: Radiological Society of North America 2008, Chicago, Nov. 30-Dec. 5, 2008. Kathy Schilling, MD, director of breast imaging and intervention, Center for Breast Care, Boca Raton Community Hospital, Fla. Stamatia Destounis, MD, spokesperson, Radiological Society of North America; Elizabeth Wende Breast Care, Rochester, N.Y.
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