The Role of MRI Imaging

Randomized trials have clearly shown that the use of screening mammography can reduce the mortality associated with breast cancer by at least 24%. A breast cancer is detected in every 2-3 women out of 1,000 who undergo routine mammography, and in the initial mammograms of 5-7 women out of 1,000. While mammography clearly detects early cancers before they can be detected on breast physical exam, it clearly misses up to 10% of cancers. What can we do to improve our detection rates of these early, curable cancers. Ultrasound evaluation provides an additional technique for examining the breast. However, both techniques are detecting a solid growth, or interruption in the normal breast tissues by a cancerous growth. Can we detect earlier stage malignancies or precancerous growths more reliably?

Magnetic resonance imaging (MRI) provides information about the blood supply to breast tissue that cannot be seen on mammography or breast ultrasound. In breast cancer, as is true for many other cancers, there is the development of extra blood vessels around a tumorous growth. This is evaluated on MRI with the use of a dye injected into the bloodstream called gandolinium. The appearance of the dye in an area of the breast, and how quickly it disappears after injection has been shown to correlate well with the presence of malignancy. Thus this technique is more sensitive than other breast imaging techniques for the detection of cancerous growths.

What are the problems associated with MRI imaging, and why is it not currently used more frequenlt? While it is a very sensitive test, the findings are not always reliable, or true tumors—the specificity of the test is not that high, resulting in false positive findings. Thus, there has been reluctance to use this technique that is very sensitive, but not always accurate, in detecting early breast cancers.

There are specific clinical situations where MRI has been proven to be very effective. It is currently used in the evaluation of women with breast implants, as it is the best techniques for detecting leaks or breaks in the implants. It is also very useful in the evaluation of women whose breast cancer first appears as an enlarged, malignant lymph node in the axilla—in the past, if no cancer was seen on mammography, these women routinely underwent mastectomy. Now, with the use of preoperative MRI, often a primary breast cancer can be identified, and breast-conserving therapy, rather than mastectomy, can be offered to these women.

Another area of interest is in women who are carriers of the breast cancer genes (BRCA1&2). These women have a life-long risk of 60-80% of developing breast cancer, and a technique that detects these cancers earlier is very important in their care. In this situation, a false positive result is also more acceptable (New England Journal of Medicine, July 29, 2004: (www.nejm.org)