WEDNESDAY, March 28, 2007 (HealthDay News) -- Women who have already been diagnosed with breast cancer should have a magnetic resonance imaging (MRI) scan of the other breast in addition to mammography. Doing so may help doctors find a small number of cancer cases missed by mammography, a new study reports.
The study found that MRI scans picked up 3 percent of cancers missed by mammography alone in women who had already been diagnosed with cancer in one breast.
"The results of this study will lead to changes in practice," said Dr. Etta Pisano, one of the study's authors, and director of the Biomedical Research Imaging Center at the University of North Carolina at Chapel Hill School of Medicine. "While this study does not suggest that MRI supplants mammography, I think what will end up happening is that all women with breast cancer will end up getting MRI" if they've had a normal mammography.
In fact, the American Cancer Society issued new guidelines Wednesday that recommend an annual MRI screen in addition to an annual mammography for women at high risk of breast cancer.
But, because the false-positive rate of MRIs was relatively high -- about 11 percent in the new study -- the authors don't recommend MRI as a screening tool for the general population.
For the new study, Pisano and her colleagues performed MRI scans on 969 women who had recently been diagnosed with breast cancer in one breast. Mammography did not detect abnormalities in the other breast of the women.
One hundred and twenty-one women had positive MRI findings, meaning they had suspected cancer in the other breast. Biopsies were done to confirm the cancer diagnosis.
Of those women, 30 were found to have cancer in the second breast -- cancers that hadn't been detected with mammography.
But, the test wasn't perfect. It had a false-positive rate of 10.9 percent.
"The costs of false-positives have to be weighed against the cost of missing a cancer," explained Pisano, adding that for women who've already been diagnosed with breast cancer, the additional knowledge gained from the MRI outweighs the false-positive risk.
"For these women, because they're at such high-risk, everything is worrisome. You really want to know that you're going to give them cancer therapy once, rather than twice," she said.
The results are published in the March 29 issue of the New England Journal of Medicine.
In an accompanying editorial in the journal, Robert A. Smith, director of cancer screening for the American Cancer Society (ACS), said the false-positive risk "is likely to be acceptable to women with unilateral breast cancer, since they will place a high priority on a thorough evaluation for the presence of other primary lesions."
Debbie Saslow, director of breast and gynecological cancers for the ACS, said that because of the high false-positive rate, she's "doubtful there will come a time when we recommend both mammography and MRI regardless of risk."
For the average-risk woman, she said, mammography is the screening tool of choice. And, Pisano pointed out that mammography can pick up very early cancers that an MRI scan may miss.
However, the cancer society is recommending an MRI in addition to mammography for high-risk women, such as those with a known genetic mutation that increases the risk of breast cancer.
In the new guidelines, the cancer society is recommending an annual MRI screen in addition to an annual mammography for women who:
- have a BRCA 1 or 2 mutation, or are untested for these mutations but have a first-degree relative with a BRCA 1 or 2 mutation;
- have a lifetime breast cancer risk higher than 20 percent (ask your doctor to assess your risk using standard risk assessment tools);
- have a known genetic mutation in the TP53 or PTEN genes or have a first-degree relative with either mutation;
- received radiation treatment to the chest between the ages of 10 and 30.
Saslow noted that these high-risk women represent only about 2 percent of the entire U.S. population, so, for most women, these new guidelines don't apply. An annual mammogram is all they need to effectively screen for breast cancer.
"So many women are so fearful of breast cancer, but most women aren't at high risk. Since most women aren't in this category, they need to remember that mammography is a really good test," said Saslow, adding, "All women need to get a mammogram every year, starting at age 40."
More information
To learn more about breast cancer screening methods, visit the American Cancer Society.
