Mammogram vs MRI: Breast Screenings For High Risk Women

By Dr. Priscilla Slanetz, radiologist specializing in breast imaging at Beth Israel Deaconess Medical Center

A number of studies published in the last few years have left many women wondering if MRI technology might be better than mammography for the detection of early breast cancers.

After all, mammograms aren't perfect: they do use low doses of radiation to image the breast and they can miss some tumors. Magnetic Resonance Imaging (MRI) is known to be more sensitive than mammography at detecting nearly all invasive cancers and a majority of in-situ (noninvasive) cancers. It certainly can find some tumors that mammography misses. And since MR uses a magnet to image the breast, it does not involve any radiation exposure.

A study in the New England Journal of Medicine in 2007 looked at 969 women who had already been diagnosed with cancer in one breast, and found that in 3.1 percent of these women, MRI found cancer in the other breast that didn't show up yet on mammogram. In addition, after review of more recent studies, the American Cancer Society recently recommended that any woman with a greater than 20-25% lifetime risk for breast cancer should consider undergoing screening with both mammography and breast MRI.  These high risk women typically fell into one of three categories: 1) known carriers of the BRCA-1/2 gene mutation; 2) women with multiple first degree relatives with breast and/or ovarian cancer; or 3) Hodgkin's lymphoma survivors who received radiation to their chest prior to age 30 years.

Although MR is more sensitive than mammography, there can be false positives with this technology which could lead to follow-up imaging and/or biopsies, revealing benign changes in the end.  Since some of these false positives are related to normal hormonal fluctuations, it is important to perform this study at the correct time of the menstrual cycle (between days 5-15).

Yet, it is also important for women to be aware that although MRI is not a perfect test, it does offer the advantage of finding cancers, often earlier than mammography.  But MR does not replace mammographic screening – it is complementary.

So why is there such controversy? Unlike screening mammography, which has been shown to reduce mortality from breast cancer by up to 30% in women ages 40 to 74, no study has yet been performed to document overall mortality reduction from breast MR screening, mainly because it is a relatively new technology and the fact that it is not standardized in the United States. The test is also expensive (costing approximately five to eight times more than a mammogram), and given current healthcare expenditures, this contributes to some reluctance to have all women undergo this study.

So who should undergo breast MR imaging?  For the past decade, women have been undergoing breast MR to detect rupture of silicone breast implants and this still is one of the indications.  Current data also supports its use for women who are considered to be at high risk for breast cancer (those with a greater than 20-25% lifetime risk). In addition, selected patients with newly diagnosed breast cancer may benefit from MR preoperatively as it often can better outline the area of involvement, minimizing the need for multiple surgical procedures.

Other patients who benefit from the study include: women with a metastatic lymph node where the primary tumor is unknown; newly diagnosed cancer patients who might be eligible for partial breast irradiation; selected patients where breast cancer recurrence is suspected clinically or on other imaging; and  selected women with incompletely characterized findings on mammography and/or ultrasound.

Women who are unable to undergo breast MR might include those who have pacemakers, have poor renal function, have metal in their bodies, or have allergies to the contrast agent.

The tough question is how to handle women who are considered to be of intermediate risk for breast cancer.  As there is no sufficient data to recommend the routine use of MR screening in this population, the addition of MR screening should be individualized to the patient whereby the benefits of early detection are weighed against the possibility of a false positive study.

And finally, if the woman chooses to add breast MR to her screening regimen, it is important to go to a facility with experience in this technology and a facility that has the MR-compatible biopsy system that would allow prompt sampling of any suspicious finding.  Using a facility with this type of experience maximizes the chance of earlier detection while minimizing the false positives.

Above content provided by Beth Israel Deaconess Medical Center. For advice about your medical care, consult your doctor.