Dr. Susan Love Research Foundation | Breast Cancer

A large study by researchers in the Netherlands has found that magnetic resonance imaging (MRI) screening is better than mammography screening in detecting tumors in women who are at high risk for breast cancer.

But although the MRIs found more cancers, they also led to twice as many unneeded additional examinations as did mammography (420 versus 207) and three times as many unneeded biopsies (24 versus 7).

Doctors at six cancer centers in the Netherlands conducted the study, "Efficacy of MRI and Mammography for Breast-Cancer Screening in Women with a Familial or Genetic Predisposition." It was published in the July 29, 2004, issue of the New England Journal of Medicine.

The study enrolled 1,909 women between the ages of 25 and 70. All of the women either carried a genetic mutation (354 women had a BRCA1 or BRCA2 mutation; 4 had mutations in a tumor-suppressor gene) or had a strong family history of the disease. Because of their genetic predisposition or family history, all of the women had at least a 15 percent cumulative lifetime risk of developing breast cancer.

During the study, the women were given a clinical breast exam every six months. They also had a mammogram and an MRI performed annually. Whenever possible, the mammogram and the MRI were done on the same day or in the same time period (between day 5 and day 15 of the menstrual cycle).

Mammograms are two-dimensional X-rays that produce pictures of the soft tissue within the breast. An MRI machine is basically a big magnet that takes advantage of the electromagnetic qualities of the body's cells. To detect cancer cells, a dye must be injected into a woman's veins prior to the MRI procedure. The dye travels through the body and is picked up most rapidly by lesions, like cancerous tumors, that have lots of blood vessels. These lesions can then be seen on the three-dimensional picture of the breast produced through MRI.

After following the women for an average of nearly three years, the researchers found 51 tumors—44 invasive breast cancers, 6 cases of ductal carcinoma in situ (DCIS), and 1 non-Hodgkin's lymphoma. One case of lobular carcinoma in situ (LCIS) was also found. Of the 50 breast cancers that were detected, 45 were included in the analysis (5 were excluded for various reasons).

MRI screening detected 32 of the 45 breast cancers (22 of these were not visible on mammography); 13 were missed by MRI (8 of these were visible on mammography, including 5 cases of DCIS; 4 were cancers that were found between the routine screenings; and 1 tumor was detected through clinical breast exam).

Mammography screening detected 18 of the 45 breast cancers (10 of which were visible on MRI) and missed 27 tumors (including the 22 that were visible on MRI, the 4 interval cancers, and the one that was detected by clinical breast exam). Mammography, however, proved better at detecting DCIS. Five of the six (83 percent) DCIS cases were detected through mammography, while MRI only detected one out of the six (17 percent) DCIS cases.

To determine a test's value as a screening tool, researchers assess its "sensitivity" and "specificity." A test that is highly sensitive produces few false negatives (women told they don't have cancer when they really do). In this study, the overall sensitivity was 17.8 percent for clinical breast exam, 40 percent for mammography, and 71.1 percent for MRI. When looking solely at the ability to detect invasive cancer, the sensitivity was 17.9 percent for clinical breast exam, 33.3 percent for mammography, and 79.5 percent for MRI.

A test that is highly specific produces few false positives (women told they have cancer when they really don't). The specificity was 98.1 percent for clinical breast exam, 95 percent for mammography, and 89.8 percent for MRI.

Thus, while MRI was more sensitive (it found more cancers), mammography was more specific (it was less likely to say cancer was present when it wasn't).

In addition to looking at which screening method was best for finding breast cancer, the researchers wanted to know whether these screening methods allowed breast cancer to be detected at an earlier stage. To answer this question, they compared the tumors discovered in the study with those discovered in two other groups: all women who had breast cancer diagnosed in 1998 in the Netherlands, and women participating in a study on breast mutations.

The researchers found that the tumors identified in the group of women they studied were significantly smaller and less likely to be node-positive than were those in the other two groups.

The researchers also found a difference between women who carried a genetic mutation and those with a family history. When large tumors (greater than 2cm) were found, they were more likely to be found in the women who carried a mutation. In addition, women who carried a mutation were more likely to have a Grade 3 tumor. (The tumor's grade is based on how abnormal its cells appear to a pathologist examining them under a microscope. A Grade 3 tumor is thought to be more aggressive than a Grade 1 or 2 tumor.)

Based on their findings the researchers conclude that MRI screening is best at detecting tumors in women at high risk for breast cancer, but that it has drawbacks as well: a high rate of unneeded additional exams and biopsies. They also suggest that for women who carry a breast cancer gene mutation, screening with MRI and mammography may need to take place more than once a year.

Susan says:
MRI has been used in the medical setting for the past two decades. Only in the last six years, though, has it been used to aid in a breast cancer diagnosis after a lesion has already been found with mammography or ultrasound. MRI also has proven to be the best tool for determining if silicone breast implants have leaked.

This study by researchers in the Netherlands supports the use of MRI for screening women who are at high risk for breast cancer because they carry a gene mutation or have a strong family history of the disease. For these women—and only these women—it is clear that adding MRI screening to mammography screening can help detect breast cancer.

There are two things women need to be aware of: MRI should not replace mammography. As this study found, mammography was able to detect some cancers that MRI missed. Mammography is also a much better tool than MRI for detecting DCIS.

Secondly, MRI is not a perfect screening tool, and women at high risk for breast cancer may find that undergoing MRI screening may lead them to have unnecessary additional exams or biopsies. However, having to deal with these possible scares may be less important for high-risk women, especially those who carry a breast cancer gene mutation, if they know the benefit is an increased chance of finding a cancer early.

No study has found that MRI is a good screening tool for women who don't have a family history of breast cancer or carry a genetic mutation. For these women, mammography remains the best screening tool, and MRI should only be used when needed to aid in a breast cancer diagnosis.