A breast MRI should not be performed to determine if the tissue is non-cancerous (benign) or cancerous (malignant). When an abnormality is found, a breast biopsy should be done to test the suspicious tissue.

Keep in mind, there can be false positive test results. And, a breast MRI cannot effectively detect small flecks of microcalcifications (calcium). These microcalcifcations account for nearly half of all cancers that mammography will detect.

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For certain women at high risk for breast cancer, screening magnetic resonance imaging (MRI) is recommended along with a yearly mammogram. MRI is not generally recommended as a screening tool by itself, because although it is a sensitive test, it may still miss some cancers that mammograms would detect. MRI may also be used in other situations, such as to better examine suspicious areas found by a mammogram. MRI can also be used in women who have already been diagnosed with breast cancer to better determine the actual size of the cancer and to look for any other cancers in the breast.

Magnetic resonance imaging

MRI scans use magnets and radio waves instead of x-rays to produce very detailed, cross-sectional images of the body. The most useful MRI exams for breast imaging use a contrast material (called gadolinium) that is injected into a catheter in a vein (IV) in the arm before or during the exam. This improves the ability of the MRI to clearly show breast tissue details.

Although MRI is more sensitive in detecting cancers than mammograms, it is more likely to find something that turns out not to be cancer (called a false positive).False-positive findings have to be checked out to know that cancer isn’t present, which means coming back for further tests and/or biopsies. This is why MRI is not recommended as a screening test for women at average risk of breast cancer, as it would result in unneeded biopsies and other tests in a large portion of these women.

Just as mammography uses x-ray machines that are specially designed to image the breasts, breast MRI also requires special equipment. Breast MRI machines produce higher quality images of the breast than MRI machines designed for head, chest, or abdominal MRI scanning. However, not all hospitals and imaging centers have dedicated breast MRI equipment available. It is also important that screening MRIs be done at facilities that can perform an MRI-guided breast biopsy. Otherwise, the entire scan will need to be repeated at another facility when the biopsy is done.

MRI is more expensive than mammography. Most insurance that pays for mammogram screening also will probably pay for MRI for screening tests if a woman can be shown to be at high risk, but it’s a good idea to check first with your insurance company before having the test. It can help to go to a center with a high-risk clinic, where the staff can help getting approval for breast MRIs.

What to expect when you get a breast MRI

MRI scans can take a long time—often up to an hour. For a breast MRI, you have to lie inside a narrow tube, face down, on a platform specially designed for the procedure. The platform has openings for each breast that allow them to be imaged without being compressed. The platform contains the sensors needed to capture the MRI image. It is important to stay very still throughout the exam.

Lying in the tube can feel confining and may upset people with claustrophobia (a fear of enclosed spaces). The machine also makes loud buzzing and clicking noises that you might find disturbing. Some places will give you headphones with music to block this noise out.

Mammograms alone failed to detect the early cancers in a study of more than 2,000 high-risk women, according to the findings.

“What my study is showing is that high-risk women should be screened earlier, beginning at the age of 30,” said study researcher Anna Chiarelli, a senior scientist at Cancer Care Ontario. “They should be screened often — every year — and they should be screened with both a breast MRI and a mammogram every year.”

Chiarelli and her colleagues followed 2,207 women, aged 30 to 69, all at high risk of breast cancer, to determine the effect of the two screenings. The women were enrolled in the Ontario Breast Screening Program, which expanded in July 2011 to screen high-risk women in a special program that uses both tests — MRI and digital mammography.

The women were viewed as high risk mainly if they had a known genetic mutation in the BRCA 1 or 2 gene, or other breast cancer-related genes; if they had not been tested for the mutations but had a first-degree relative with them; if they had a family history of breast cancer and personally had a 25 percent or higher lifetime risk; or if they had radiation therapy before age 30.

The first-year results of the high-risk program turned up 35 breast cancers. None of them was detected by mammogram alone; 23 were detected by MRI alone, and another dozen were picked up from both screenings.

“If we only had offered these women mammograms, we would not have found 23 of these breast cancers,” Chiarelli said.

In some cases, the mammogram was positive, in others, it was negative, she added. But in all the cases of breast cancer diagnoses, the MRI was positive.

The study is published in the June 16 online edition of the Journal of Clinical Oncology.

Some U.S. experts, including those at the American Cancer Society, also recommend both tests for high-risk women.

“The combination [using two tests] was important,” said Dr. Otis Brawley, chief medical officer of the American Cancer Society, who reviewed the findings. The society advises both tests be done annually in high-risk women.

He noted that the Canadian researchers looked at a rigorous program of screening with experienced doctors who read MRIs and mammograms correctly.

In the United States, some insurance plans will pay for both tests if a woman is at high risk, Brawley said. MRIs, which are much more expensive than mammograms, can cost $2,000 or more for both breasts.

Women do need to know that MRIs, which use magnets and radio waves, not radiation, may find suspicious lesions that turn out to be noncancerous, just as mammograms sometimes do, Brawley said.

The findings of the Canadian study apply only to high-risk women, not the majority of women. About 5 percent to 10 percent of breast cancers are linked to genetic defects, the society estimates.

More information

For more on breast cancer testing recommendations, visit the American Cancer Society.