More than 275,000 women in the US will be diagnosed with breast cancer this year, and 40,110 will die of the disease. Routine use of screening mammography in the general population (women ages 50 to 70) has been shown to reduce breast cancer-related mortality by at least 24%. On average, American women have a one in eight chance of developing breast cancer, but some subgroups are at disproportionate risk. Women at highest risk― those with a strong family history of, or genetic predisposition for, breast cancer—have a 51% chance of being diagnosed by age 50, and an 85% chance by age 70. As well, these women often develop aggressive, rapidly growing cancers at a young age.

In highly susceptible women, preventive mastectomy , preventive oophorectomy (removal of one or both ovaries), chemoprevention (drug therapy to lower the risk of disease), and yearly mammography screening beginning at age 25–35 can help prevent or make an early diagnosis of breast cancer. Mammography, however, detects less than half of the breast cancers in women with a genetic tendency, perhaps owing to infrequent screening, dense breast tissue at young age of screening, and unusual features of their cancer tumors. Since magnetic resonance imaging (MRI) is essentially uninfluenced by breast density and provides some information that mammography cannot, it has recently been studied as a screening tool for breast cancer in high-risk women.

In the July 25, 2004 issue of the New England Journal of Medicine , researchers in the Netherlands compared breast examination by a health professional, mammography, and MRI in high-risk women. Of these, they found that MRI was by far the most sensitive screening tool.

About the Study

The study recruited 1,909 women, ages 25-70, from six cancer clinics in the Netherlands from 1999 to 2003. All of the women had an overall lifetime risk of breast cancer of 15% or higher due to family history or genetic predisposition.

Enrolled women underwent clinical breast examinations every six months, and imaging studies― both mammograms and MRIs― annually (and concurrently). The researchers who interpreted the mammograms were not aware of the MRI results, and vice versa. Whenever an examination reported a possible tumor, further investigation was performed, and final diagnosis of malignant tumors was based on microscopic examination of breast tissue.

To determine whether the screening protocol used in this study was able to identify cancers at an earlier stage than traditional screening protocols, researchers compared results from this study with data from Dutch breast cancer patients of the same age in two other studies.

The Findings

After three years, breast cancers were found in 2.7% of the women (51 malignant tumors). Thirty-two breast cancers were found by MRI (22 of which were not visible by mammography), while 18 breast cancers were found by mammography (eight of which were not detected by MRI). The overall sensitivity of the three tested screening tools was 18% for clinical breast examination, 40% for mammography, and 71% for MRI. This means that if breast cancer was present, the MRI detected it 71% of the time.

Besides being the most sensitive screening tool studied, MRI was also better able to discriminate between and benign cancers, although mammography was better able to detect less invasive breast cancers. Furthermore, the tumors detected in this study were on average smaller and less likely to have spread to the lymph nodes than the tumors detected in the comparison studies.

While MRI appeared to thoroughly outperform mammography, it’s higher sensitivity came at a price: the MRI was more likely to incorrectly “find’ a cancer that was not really there. This lower specificity leads to more unnecessary follow-up investigations, anxiety, and costs.

How Does This Affect You?

Compared to mammography, MRI appears to be better able to identify breast cancers in high-risk patients. Another benefit is that MRI doesn’t rely on high energy radiation, so the increased the number of tests required to screen younger women more often would not pose any health risks. The drawbacks of MRI, however, include higher cost and lower specificity. And finally, though MRI was very capable of detecting cancers at an early stage, detection does not necessarily guarantee improved survival rates for patients. A randomized, controlled trial with breast cancer mortality as the end point is the only way to prove that any screening intervention improves survival.

Until such a study on MRI is undertaken, though, it is safe to say that frequent MRI screening appears to be beneficial to high-risk women who may develop tumors at a young age. There is no evidence to date, however, that MRI is a more effective screening test in women at normal risk. And, even there was, its high cost would make it impractical for widespread use.