In a new study of women at increased risk for breast cancer, adding an ultrasound examination to routine mammography revealed 28 percent more cancers than mammography alone.

However, the ultrasound exam substantially increased the rate of false positive findings and unnecessary biopsies, according to the study published in the May 14 issue of the Journal of American Medical Association.

The Keck School of Medicine of USC was one of 21 participating sites.

The study enrolled 2,809 women at increased risk for breast cancer; the research data from 2,637 of these women were eligible for analysis.

Criteria used to determine an increased breast cancer risk included participants who were 25 years or older with a prior atypical breast biopsy and personal and/or moderate family history of breast cancer.

Forty women were diagnosed with breast cancer within 12 months of the initial screening. Mammography alone revealed 20 cancers (50 percent of all cancers detected) for a detection rate of 7.6 women per 1,000 women screened, though one cancer was dismissed.

The combination of mammography plus ultrasound revealed 31 cancers (78 percent of all cancers detected) for a detection rate of 11.8 women per 1,000 women screened.

Eight of the 40 cancers were not seen with either mammography or ultrasound at the time of the initial screening but were discovered later during the 12-month period for a rate of three cancers missed per 1,000 women screened.

The risk of incurring an unnecessary biopsy due to a false positive exam result from the supplemental ultrasound also was substantially increased in the study.

Mammography alone prompted an unnecessary biopsy for one in 40 women. The combination of mammography and ultrasound prompted an unnecessary biopsy for one in 10 women, or four times more women having an unnecessary biopsy.

According to Linda Hovanessian, associate professor of radiology at the Keck School of Medicine and site principal investigator for the study, “For women at elevated risk of breast cancer, we learned that ultrasound finds cancers not seen by mammography.

“However, we also learned that there is a significantly higher false-positive rate associated with the addition of an ultrasound exam. This means something suspicious was seen on the ultrasound which, as the result of a biopsy, turned out not to be cancer.”

The radiology department at the Keck School of Medicine has been a leader in this critically important research, she noted.

The American Cancer Society recently recommended that certain women at very high risk for breast cancer be screened with magnetic resonance imaging in addition to mammography, and these results do not change that recommendation.

Women should talk with their doctor about their breast cancer risk profile and whether an ultrasound exam supplemental to mammography might be beneficial, keeping in mind the potential for a false positive result and an unnecessary biopsy.

At present, there is a limited supply of trained personnel and facilities offering ultrasound. Women also should consult their health insurance policies regarding the coverage for breast cancer screening options. An annual mammogram is still recommended. Neither MRI nor ultrasound is meant to replace mammography.

The study was made possible through funding from a novel private-public partnership between the Avon Foundation and the National Cancer Institute, part of the National Institutes of Health.