With MRIs, no clear picture of effectiveness
The fight against breast cancer appears to have a new tool: magnetic resonance imaging (MRI) scans. On March 27, the American Cancer Society issued new guidelines that recommend MRIs in conjunction with yearly mammograms for certain women.
But who should get these tests, and do the costs -- both financially and emotionally -- outweigh the benefits?
Known largely for their use in imaging active areas of a person’s brain, MRI scans generally measure tissue density. Because cancerous regions differ in density from normal tissue, MRI scans can also be used to detect cancers in tissue other than brains.
An advisory board of the American Cancer Society analyzed studies that looked at whether MRIs can pick out tumors in women’s breasts and decided that for a small group of women at high risk for getting breast cancer, MRIs can be quite helpful in finding small tumors. A study published the same week in the New England Journal of Medicine reported that MRIs found undetected cancers in the other breast of 3% of women who were newly diagnosed with breast cancer.
Even before release of these findings and the American Cancer Society’s recommendations, discussion of MRI usage in breast cancer screening had created confusion and concern, experts say. Adding to the muddle, last week the American College of Physicians released a statement challenging the need for routine mammograms for women younger than 50, and a new study questioned the effectiveness of computerized mammography, a higher-tech mammogram, in detecting tumors.
If MRI scans are better than mammograms at detecting tumors in women, isn’t the MRI a superior test, and shouldn’t all women get one, not just women at elevated risk? “I’ve even been getting e-mails from doctors wondering about this,” says Dr. Joann Elmore, an internist at the University of Washington School of Medicine in Seattle.
But Elmore says the recommendations are clear: “The great majority of women in the United States should not be getting MRI scans for breast cancer screening.”
The test, cancer experts say, is very expensive -- about 10 times the cost of a mammogram. Women who aren’t high risk would probably have to pay for it out of pocket, they add. And in any case, its benefit for women with low cancer risk is unknown. “The value of MRIs has not been studied in the average population,” Elmore says.
Thirdly, the test isn’t perfect: MRI scans can pick up non-cancers in women, as well. These false positives can lead to unnecessary testing and even invasive biopsies. This happens with mammograms too, just not as often.
“False positives occur with all screening,” says Dr. Christy Russell, co-director of the Norris Breast Center at USC and chairwoman of the American Cancer Society’s Breast Cancer Advisory Group.
“The higher your risk, the more likely you are to accept false positives as a trade-off for finding cancer,” Russell adds.
If most women shouldn’t seek out an MRI test, who should? “The only way to get into that [MRI screening] bracket is to have a significant family history of breast cancer,” Russell says.
That means more than just having a relative with breast cancer. A woman would be considered at high risk if at least two women in her family -- her mother, sisters or daughters -- have breast cancer or a combination of breast cancer and ovarian cancer before age 50.
A woman would also be considered high risk if she carries certain mutations in her BRCA1 or BRCA2 genes. Mutations in these genes (or other as yet unidentified genes that confer high risk of early breast cancer) cause less than 10% of breast cancer cases. But 65% of women with BRCA1 mutations, and 45% of women with BRCA2 mutations, have breast cancer by age 70.
Of all U.S. women between the ages of 30 and 70, the number of women the new guidelines affect might be between 1 million and 1.5 million women, Russell says. They should consider having an MRI in conjunction with their yearly mammograms.
Crunching the numbers for cancer risk in these cases works out to a 20% to 25% risk or greater of getting breast cancer over a woman’s lifetime. This 20% to 25% number arose because these were the types of women in the studies the cancer society examined in crafting its recommendation, says Dr. Constance Lehman, a radiology professor at the University of Washington.
Any woman reading the new guidelines might be curious to know what her risk is. Several so-called “risk assessment” tools are available to doctors or individuals -- but none is perfect.
The various tests measure somewhat different things. For example, a user-friendly “Breast Cancer Risk Assessment Tool” at the National Cancer Institute’s website (www.cancer.gov/bcrisktool) determines a woman’s risk based largely on reproductive data. Except for those 10% who have strong family histories, lifetime estrogen exposure is believed to be the most significant factor in determining breast cancer risk.
After plugging in numbers such as the age at which she first started menstruating and the age at which she first gave birth, the test spits out both her chances of developing breast cancer in the next five years and by the time she turns 90.
The tool does not go into much detail about family history, and for that reason would not be used by physicians to determine whether she’s a candidate for an MRI.
A woman who suspects that some genes in her family put her at high risk will have to go further. Other tests are available to physicians. One, called BRCAPRO, allows them to plug in information about a woman’s family history of breast and ovarian cancer to determine the likelihood that she is a carrier of a BRCA gene mutation.
In addition, some healthcare organizations employ genetic counselors, who can advise patients about what their genes tell them.
Russell says it’s important for primary care physicians to bone up on what makes a woman high risk -- and thus, whether an MRI is for her. She is concerned that some physicians will not get it right because the technology is so new.
“The people who will have to order the tests are not cancer specialists,” she says.
For concerned women, Lehman says, the National Cancer Institute’s website is a good place to begin gathering data. But then, she adds, a woman needs to talk to her doctor.
