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However, ultrasound has a downside: risks of false positive results and unnecessary biopsies that may outweigh the scans’ benefits.

The study, based on a three-year, multi-center trial, appears in the Journal of the American Medical Association.

“In women at high risk for breast cancer with mammographically dense breasts, magnetic resonance imaging (MRI) is a more effective supplement to mammograms than ultrasound,” says co-author Dione Farria, a breast imaging radiologist at the Alvin J. Siteman Cancer Center at Washington University in St. Louis School of Medicine and Barnes-Jewish Hospital.

A portion of the 2,700 subjects were seen at the Joanne Knight Breast Health Center at the Siteman Cancer Center. All participants received yearly mammograms over the course of three years; in addition, researchers scanned the study participants annually with ultrasound.

Ultrasound detected additional cancers and substantially increased the number of recommended biopsies and follow-up studies. At the first exam, adding screening ultrasound resulted in a 15 percent increase in imaging workups and a 7.8 percent increase in biopsy recommendations.

However, significantly fewer of the women sent for biopsies on the basis of ultrasound alone had cancer compared with those who had biopsies based on mammography results.

After three rounds of screening with mammography and ultrasound, 600 subjects had screening contrast-enhanced breast MRI. The additional MRI scans detected cancer in about 1.5 percent of these women, even though they had normal mammograms and ultrasounds for three years.

This means the cancer yield from adding MRI scans is four times greater than that provided by adding ultrasound.

All of the ultrasounds in the study were performed by breast imaging specialists. The results may not apply to many clinical practices because they commonly rely on non-physicians or automated systems to perform ultrasound exams. Additional patient workups and false-positive (non-cancer) biopsies may occur more frequently when breast imaging specialists are not performing the studies, the researchers suggest.

Since the study recruited women who were of higher-than-average risk for breast cancer, these results do not apply to women with average risk, even if they have dense breasts.

“As physicians, we have to carefully weigh the benefits of additional tests to detect cancer against the chance of requesting potentially unnecessary biopsies,” Farria says. “We must also remember that ultrasound and MRI do not replace the need for annual mammography. They are tools physicians sometimes use to supplement mammography.”

According to the American Cancer Society, women with a 20 percent to 25 percent or higher lifetime risk for breast cancer should obtain annual breast MRI screening in addition to annual mammography.

Farria says the Joanne Knight Breast Health Center has no current plan to offer screening ultrasound for breast cancer.

The study was conducted through American College of Radiology Imaging Network (ACRIN), with funding from The Avon Foundation and the National Cancer Institute.

More news from Washington University in St. Louis: http://news-info.wustl.edu/