MRIs may be better at detecting breast cancer

Women with a family history of cancer may be better off getting an MRI than a mammogram, the more common test to screen for the disease that strikes more than 200,000 United States women every year, a new study showed.

A group of Dutch researchers found that MRI scans, which use strong magnetic and radio waves to produce pictures of the body from any angle, have an 80 per cent success rate of detecting cancer, far higher than other tests.

"MRI appears to be more sensitive than mammography in detecting tumours in women with an inherited susceptibility to breast cancer," said the team, led by Mieke Kriege of the Rotterdam Family Cancer Clinic in Holland.

The group reported its findings in Thursday's New England Journal of Medicine.

Breast exams found the cancer only 18 per cent of the time while the mammograms, X-ray tests that produce an image of the breast, worked in 33 per cent of the cases, the doctors found.

However, MRIs are also more likely to sound a false alarm and they are significantly more expensive than other tests.

The study, begun in late 1999, surveyed 1,909 women in the Netherlands who all had a greater-than-average risk of getting breast cancer. All received annual mammograms and MRI scans, plus standard physical exams.

Of 40 cancers found in the study, 55 per cent were spotted by MRI alone, 20 per cent were found by mammogram alone, and 25 per cent were identified by both techniques, the study showed.

But the MRI also showed suspicious results in 10 per cent of the women who did not have cancer, indicating a false positive rate that was twice as high as that of mammograms.

"Screening by MRI led to twice as many unneeded additional examinations as did mammography, and three times as many unneeded biopsies," Kriege's team said,

But researchers said an MRI may be particularly helpful to women whose DNA harbour mutations that make them prone to breast tumours.

Although 1 in 7 US women will be diagnosed with breast cancer in their lifetime, 85 per cent of women with a breast cancer mutation known as BRCA1 will develop breast cancer by age 70.

Mammograms may be less effective in those women for several reasons, said Laura Liberman in a Journal editorial. One may be that tumours caused by BRCA mutations seem to grow faster. Another may be that those women tend to get cancer at a younger age, when their firmer breast tissue makes it hard to spot cancer using X-rays.

But for women with the breast cancer mutation, Liberman said, the greater sensitivity of an MRI scan may outweigh the drawback of the false positives.

"MRI may also be valuable in screening women with an increased risk due to nongenetic factors, such as prior breast cancer," she said, "but more work is needed to substantiate this possibility."

Of the 1,909 women in the study, 88 underwent surgery to have their breasts removed before cancer was found out of fear that they would develop a tumour. Eighty-nine women stopped having MRI scans because of claustrophobia or other reasons.

- REUTERS