The American Cancer Society estimates that close to 216,000 women will be diagnosed with breast cancer in 2004. While the cause of most breast cancers is unknown, up to one in every ten cases is believed to result from a genetic mutation, which is an abnormal change to a gene passed from parent to child. BRCA1 and BRCA2 are the most common mutations associated with breast cancer. A woman with one of these mutations has an 85% risk of developing breast cancer during her life—this roughly seven times the risk of a woman without a mutation.

To combat this high risk, some women have their healthy breasts surgically removed, which is called prophylactic mastectomy . This procedure can reduce the risk of breast cancer by 90% or more, but it carries significant negative physical and psychological effects. Women who choose to keep their breasts are advised to undergo regular breast cancer surveillance. Surveillance begins as early as age 18 with a clinical breast exam (CBE) every six months and, starting at age 25, an annual mammogram. These screening tests must be done indefinitely.

Despite intensive efforts at early detection, many cancers in BRCA carriers are discovered in advanced stages. Certain features of these tumors allow them to elude mammography. Those that may look harmless on a mammogram can still grow quickly, and they usually affect younger women who have denser breasts, which are harder to examine via mammography. Investigators have been interested, therefore, in studying other methods to enhance the effectiveness of mammography. Two such techniques are already widely available: magnetic resonance imaging (MRI) and ultrasound. MRI uses magnetic waves and ultrasound uses high-frequency sound waves to generate images of breast tissue non-invasively.

In a study published in the September 15, 2004 issue of the Journal of the American Medical Association , a group of researchers from Toronto, Canada, compared the accuracy of MRI , ultrasound , mammogram , and clinical breast exam (by a trained health professional) for detecting breast cancer in women who carry the BRCA1 or BRCA2 gene mutation.

About the Study

The researchers recruited 236 Canadian women between the ages of 25 and 65 who have the mutation BRCA1 or BRCA2 . After completing a questionnaire, the women were given all four screening exams on one day—clinical breast exam (CBE), mammogram, ultrasound, and MRI. As long as they remained in the study, the CBE was repeated every six months, and the other three exams were repeated once a year. Time spent in the study ranged from one to three years.

The researchers checked in with each woman one year after her last screening exam. The women filled out a questionnaire and reported any incidences of cancer or prophylactic mastectomies. After compiling all the data—results of each screening exam and responses to the questionnaires—the researchers compared the accuracy of each screening exam individually and in combination.

The Findings

More cancers were detected by MRI than any other screening method used alone. Of the 22 cancers that developed among the women in this study, 77% were detected by MRI, 36% by mammogram, 33% by ultrasound, and 9.1% by CBE.

This study also found that the likelihood of accurately finding a cancer (sensitivity) increased as more screening methods were used:

Mammography + CBE = 45% sensitivity

Mammography + CBE + ultrasound = 64% sensitivity

Mammography + CBE + MRI = 86% sensitivity

Mammography + CBE + ultrasound + MRI = 95% sensitivity

All of the women who were diagnosed during the study were treated and are now cancer free.

How Does This Affect You?

These findings apply only to women with BRCA1 or BRCA2 genetic mutations. The dramatic increase in breast cancer detection confirms what previous studies have suggested—that MRI is a valuable tool for this group of high-risk women. One question that needs further investigation is whether the increased detection of breast cancers will translate into longer life. Talk with your doctor about including MRI in your surveillance plan if you are a BRCA carrier.

For women of average breast cancer risk, the benefits of MRI screening do not appear to be as great. Despite its limitations, mammography is still considered the best screening method for such women, particular those over 50. Discuss with your doctor the most appropriate time to start regular mammogram screenings.