One included 445 women with BRCA mutations who were recruited for an MRI study at the University of Toronto between 1997 and 2007. The women underwent yearly screening with MRI, mammograms, and breast exams in a doctor’s office or clinic.

The other group included 830 BRCA-mutation carriers involved in a study at 13 North American medical centers. Those women were advised to undergo yearly mammograms and clinical breast exams - although no screening regimen was formally set.

The women ranged in age from 25 to 65; the average woman was in her mid-40s.

Overall, the same proportion of women - 9 of every 100 - in each group developed breast cancer during the 6-year study.

But women in the MRI screening group were more likely to have an early-stage cancer discovered. For example, 14 of every 100 women in the MRI group were diagnosed with early breast cancer, compared to only 7 of every 100 in the comparison group.

In contrast, only 2 of every 100 women in the MRI group received a diagnosis of stage 2 to stage 4 breast cancer, compared to 7 of 100 in the comparison group.

When the research team took some other risk factors into account - such as age, oral contraceptive use, whether the women still had their ovaries, and other personal characteristics - they found that women in the MRI group were 70 percent less likely to be diagnosed with stage 2 to stage 4 cancer versus women in the comparison group.

Whether MRI screening actually saves lives is not yet known, however. Further studies are needed to look at its effects on death rates from breast cancer, according to the research team.

MRI screening is not without its downsides. Along with its greater sensitivity for spotting small tumors comes a higher risk of false-positives - suspicious findings that turn out not to be cancer upon further testing. That leads to unnecessary follow-up biopsies, added costs and, for some women, anxiety.

One study found that 8 of every 10 positive findings on MRI screening were actually false-positives.

MRIs are also much more expensive than mammograms, at $1,000 or more per test. For women with BRCA mutations, insurance generally covers the costs, but preventive mastectomy is less expensive. The surgery is done only once, whereas MRIs need to be repeated every year.

What it comes down to, according to Burness, is that women with BRCA mutations should be aware of all their options and discuss them with their doctor.

“In my mind,” she said, “that’s very empowering.”

SOURCE: Journal of Clinical Oncology, online March 28, 2011.