But False Positives Are a Problem, Study Shows
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Reviewed By Louise Chang, MD
May 13, 2008 — Adding ultrasound to mammography improves breast cancer detection in high-risk women, but the rate of false-positive findings is also much higher than with mammography alone, a new study confirms.
When ultrasound was added to mammography, 28% more cancers were found than when mammography was the only screening method used, researchers reported in the May 14 issue of The Journal of the American Medical Association.
But four times as many women who had the combination screening had false positive findings that led to unnecessary biopsies.
The study confirms that mammography and ultrasound find more breast cancers than mammography alone in high-risk women, especially those with dense breasts.
But the high false positive rate and the lack of availability of screening ultrasound for breast cancer will likely limit its role as a screening tool, says radiologist and study researcher Wendie Berg, MD, PhD, of the American Radiology Services Inc., Johns Hopkins Green Spring.
"There is a shortage of trained personnel, so if everybody decided tomorrow to use ultrasound to screen for breast cancer, that couldn't happen," she tells WebMD.
Mammography, Ultrasound, and MRI
The American Cancer Society (ACS) now recommends that women with the highest risk for breast cancer undergo annual screening with magnetic resonance imaging (MRI) in addition to mammography.
These results will not change that recommendation, but ultrasound may represent an alternative screening approach for high-risk women who do not have access to MRI or MRI-guided biopsy, says ACS Director of Breast and Cervical Cancer Debbie Saslow, PhD.
"There are no guidelines for high-risk women without access to MRI," she tells WebMD. "We have said informally that these women can consider ultrasound, but it is important that they are made aware of the high rate of false positives."
The study involved 2,637 high-risk women with dense breasts screened at 21 different centers.
Half of the women in the study had been treated for a previous breast cancer and most others had one or more close family members who had had the disease.
Forty women received a diagnosis of breast cancer within 12 months of screening. Just half of these cancers were identified by mammography alone, while the combination of mammography plus screening ultrasound revealed 31 cancers.
Eight of the 40 cancers were not seen with either screening method but were detected during the yearlong follow-up.
False positive findings resulting in unnecessary biopsy occurred in one in 10 women screened with mammography and ultrasound, compared to one in 40 women screened with mammography alone, Berg says.
The study was funded by the National Cancer Institute and the Avon Foundation.
Mammography Still Needed
In an editorial accompanying the study, radiologist Christiane Kuhl, MD, of the University of Bonn writes that the large study confirms the poor performance of mammography in high-risk women, especially those with dense breasts.
"Mammography will probably remain the basis for breast cancer screening for the foreseeable future," she writes. "However, increasing evidence suggests that for many women, mammography does not provide the best possible accuracy."
But Kuhl tells WebMD that because mammography is the best screening tool for identifying the earliest form of breast cancer, known as ductal carcinoma in situ (DCIS), it is still needed, even when ultrasound or MRI are used.
"Every woman with dense breast tissue should be offered ultrasound," she says. "That may not be practical at a population level, but that is what the evidence is telling us."
Kuhl says the issue of false positives, while troubling, is less of an issue with ultrasound than with mammography, because biopsies can often be performed during the screening with ultrasound-guided biopsy.
In her editorial, Kuhl writes that although mammography has been used for more than four decades, it may now be time to reconsider.
"Individualized screening schemes tailored to the individual risk and to the personal preferences of a woman may be the way to consider how to screen for breast cancer," she writes. "Whether in the long run, ultrasound or breast MRI will be more appropriate for this purpose remains to be seen."
SOURCES: Berg, W.A., The Journal of the American Medical Association, May 14, 2008; vol 299: pp 2151-2163. Wendie A. Berg, MD, PhD, radiologist, American Radiology Services, Johns Hopkins Green Spring, Lutherville, Md. Christiane K. Kuhl, MD, radiologist, University of Bonn, Germany. Debbie Saslow, PhD, director of breast and cervical cancer, American Cancer Society.
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