The study "also shows that ultrasound does not have added benefit compared to MRI," added Lehman.
MRIs found all six of the breast cancers detected, while mammography spotted only two, and ultrasound found just one, among the study's sample of 171 women at high risk but without symptoms of breast cancer. A larger, earlier study of women already diagnosed with breast cancer found that MRIs also detected more cancers in the opposite breast than mammography did.
In March, the American Cancer Society published new guidelines recommending both mammography and MRI screening for women at high risk for breast cancer.
The current study, published in the August issue of Radiology, does not break new ground but does add evidence on the advantages of adding MRIs to the screening process, as well as the disadvantages of adding ultrasound, according to Dr. Daniel C. Sullivan, associate director of Duke University's Comprehensive Cancer Center in Durham, N.C.
"There has been conflicting data from other small studies about ultrasound. Some found it is effective, and some have not. This [study adds] a little more information that it is not," said Sullivan, an expert on biomedical imaging. To be more conclusive, scientists are awaiting a larger study on ultrasound that is currently under way, he said.
Based on earlier studies and supported by the current study, the "data are pretty clear" about the usefulness of adding MRI to mammography screening for premenopausal women at high risk for breast cancer, Sullivan added. Only about 1 percent to 2 percent of all women fall into the high risk category, noted Debbie Saslow, director of breast and gynecologic cancer for the American Cancer Society.
The current study included 171 women averaging about 46 years of age. About 46 percent of the women were premenopausal. The researchers defined high risk in women 25 and older as a woman who carries one of the breast cancer genes BRCA1 or BRCA2 or a 20 percent probability of carrying a mutation, or a strong family history of breast and ovarian cancer.
Further research is needed to determine whether MRI should be added to screenings for older women or a broader group of women, Sullivan said. So far, using MRIs along with mammography can be justified only with high risk women because of the higher cost of MRIs, the risk involved in injecting contrast material needed to display very small lesions, and the biopsies required to rule out false-positives, he added. In the current study, the MRIs did detect eight false-positives.
For technological reasons, MRIs are often able to detect cancers that mammography misses, Sullivan explained. However, MRIs should not be seen as a replacement for mammograms, he added. In a previous study, mammography detected a few cases that were actually missed by MRI, the expert said. |
