Many women have come to rely on mammograms for early detection of breast cancer; they have provided reassurance and saved countless lives. But mammograms miss between 10 and 20 percent of malignant tumors in women over 50, and more in younger women whose dense breast tissue is hard to distinguish from cancer in the test. Researchers from the Netherlands compared the popular mammogram with magnetic-resonance imaging (MRI) scans to see which technique caught more cancers.

What the researchers wanted to know: Does MRI scanning work better than mammograms in detecting breast cancer?

What they did: The doctors sampled 1,909 women who were at moderate or high risk for breast cancer—the largest sample ever taken for a study of the effectiveness of MRI scans. All of the women had a clinical breast exam every six months, an annual mammogram, and an annual MRI scan for four years. The researchers compared how well the MRI and mammogram detected malignant growths in the breast.

What they found: MRI scans were much better at detecting breast cancer. The MRI found 71 percent of breast cancer tumors in the sample, while mammograms detected only 40 percent. Out of the 45 total cases of cancer detected, the MRI found 22 that the mammogram missed, the mammogram found 8 not seen by the MRI, and 10 were visible on both images. The other five were detected through clinical breast exams.

What it means to you: This study strongly suggests that women who are at high risk for breast cancer should have MRI screening in addition to yearly mammograms. However, most women in the United States are not at high risk and the MRI scans cost much more than mammograms–often all out of the patient's pocket. The bottom line, don't run out to your neighborhood MRI imaging center without talking to your doctor first.

Caveats: MRI screening was much more sensitive than mammograms, but it also led to more false positives and twice as many unnecessary follow-up exams. Both types of screens, it seems, are necessary in high risk women.

Find out more: The most famous breast cancer organization is the Susan G. Komen foundation, promoter of the famous pink ribbons. Their website (www.komen.org) is full of helpful information about breast cancer. Another good but less well-known site is (www.breastcancer.org) which has short articles written by experts on all kinds of breast cancer topics.

Read the article: Kriege, M. Efficacy "Of MRI and Mammography for Breast-Cancer Screening in Women With aFamilial or Genetic Predisposition." New England Journal of Medicine. July 29, 2004, Vol. 351, No. 5, pp. 427-437.

Abstract online: http://content.nejm.org