Scientists from the University of North Carolina have completed a multi-centre study which found a significant benefit in screening the other breast when cancer had been detected.

Healthy women at high risk of getting breast cancer also should get magnetic resonance imaging scans, the society said.

The recommendations follow a study that shows MRI scans can detect cancer in the opposite breast 90 per cent of the time. MRI found breast tumours missed by mammograms, a specialised type of X-ray.

The study, published in The New England Journal of Medicine, involved 1,000 women with cancer in one breast. The MRI scans found 30 out of 33 tumours in the other breast among the women.

"One in 10 women diagnosed with cancer in one breast will develop the disease in the opposite breast. Having a better technique to find these cancers as early as possible will increase the chances of successful treatment," said NIH director Elias Zerhouni.

The National Cancer Institute, one of the National Institutes of Health, paid for the study.

"This study gives us a clearer indication that if an MRI of the opposite breast is negative, women diagnosed with cancer in only one breast can more confidently opt against having a double, or bilateral, mastectomy," added National Cancer Institute director John Niederhuber.

Constantine Gatsonis and colleagues at Brown University in Rhode Island said the study was not designed to find out if MRIs or mammograms are better at finding breast cancer among women who have only an average risk.

"It was designed only to see if MRI improved detection of cancers in the other breasts of women already diagnosed with unilateral breast cancer," she said in a statement. The American Cancer Society said women with a genetic mutation that puts them at high risk of breast cancer, called a BRCA mutation, should also have an MRI scan in addition to annual mammograms.

In addition, women with a close relative with such a mutation should get an MRI, the group recommended.

And women who got radiation treatment to the chest between the ages of 10 and 30, such as for Hodgkin's disease, a lymph cancer, should have MRIs. Such treatment in the 1970s and 1980s has been shown to raise the risk of breast cancer in later life. "As with other cancer screening tests, MRI is not perfect and in fact leads to many more false positive results than mammography," noted Christy Russell of the University of Southern California/Norris Cancer Hospital Lee Breast Centre, and chair of the American Cancer Society's Breast Cancer Advisory Group.

"Those false positives, which can lead to a high number of avoidable biopsies, can create fear, anxiety, and adverse health effects, making it imperative to carefully select those women who should be screened using this technology."

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