X-Rays Linked to Breast Cancer in Women Who Carry Gene

Widely used X-ray tests have been implicated for the first time as a cause of breast cancer, apparently raising the risk in women with an inborn susceptibility, researchers report.

A study at the University of North Carolina in Chapel Hill found that moderately strong X-rays significantly raise the risk of breast cancer in women who carry a particular gene that occurs in more than 1 million American women.

The researchers say the increasing use of X-rays could help explain why breast cancer appears to have become more common in recent decades.

Since most carriers of the gene do not know they have it, the researchers said their work suggests that doctors should cover all women’s breasts with lead shields during X-rays and use non-X-ray tests whenever possible.

Until now, only relatively high doses of radiation have been clearly associated with an increased risk of breast cancer. Dr. Michael Swift, who directed the study, said the amount of radiation that appeared to trigger this cancer in gene carriers was “appallingly low.”

“It would be a lot easier world if this were not true,” Swift said. “But if it is true, it demonstrates a way to prevent perhaps 5,000 to 10,000 cases of breast cancer per year. That would be very welcome indeed.”

Swift and his colleagues at the University of North Carolina in Chapel Hill found the cancer link in people who carry the ataxia-telangiectasia, or AT, gene. They published their findings in today’s New England Journal of Medicine.

If someone inherits two copies of this gene--one from each parent--they get ataxia-telangiectasia, a rare disease that affects coordination. However, about 1.4% of Americans carry one copy of the gene and suffer no obvious effects.

Four years ago, Swift’s team showed that nearly 8% of all breast cancer in the United States could result from this gene. The latest work suggests that radiation can trigger the gene to cause cancer.

Swift’s team found an increased risk among gene carriers who received X-ray tests that probably exposed their breasts to between 0.1 and 0.9 rads of radiation. Until now, no increased risk has been seen below 10 rads.

Dr. John Boice of the National Cancer Institute said he was skeptical of the findings, however, in part because the researchers could not precisely say how much radiation the women had received to their chests.