MONDAY, June 26 (HealthDay News) -- Exposure to chest X-rays may put women who are genetically susceptible to breast cancer at an even greater risk for the disease, a European study finds.

And being exposed to any X-rays before the age of 20 may boost that risk even more, according to the research, published in the June 26 issue of the Journal of Clinical Oncology.

The retrospective study, the first to look at the BRCA gene mutation and low-level X-rays, involved more than 1,600 women who have mutations in the BRCA 1 or BRCA 2 genes, which raise lifetime risk for breast malignancy. All were asked to recall whether they had ever had a chest X-ray, and those participants who reported having one were 54 percent more likely to develop breast cancer than women who had not, the researchers found.

But the lead author of the study, David E. Goldgar, cautioned that the findings were preliminary and that more studies are needed before the relative risks and benefits of mammography, which relies on X-ray technology, could be weighed.

"We do not want to get into making specific recommendations about whether a woman should or should not have this particular screening without knowing what the benefits and risks are," said Goldgar, who was chief of the genetic epidemiology group at the International Agency for Research on Cancer in Lyon, France, when the study was conducted.

For the study, Goldgar and his colleagues asked 1,601 female BRCA 1/2 carriers to fill out questionnaires regarding previous exposure to chest X-rays. Not all women had developed breast cancer at the time of the study.

Participants with BRCA 1/2 mutations who reported ever having a chest X-ray were 54 percent more likely to develop breast cancer than women who reported never having had a chest X-ray.

And women who had had chest X-rays before the age of 20 had a 2.5 times increased risk of developing breast cancer before they turned 40, compared with women who had never been exposed to such X-rays.

Goldgar, who is now at the University of Utah, pointed out that most of the chest X-ray risk in the study affected younger women, and that even high-risk women don't start having mammograms until they are in their 30s. "Most of the risk is from exposure at younger ages," he said. "I don't think a woman should stop having mammograms at age 35."

Goldgar added, however, "It does bring up a lot of issues. That's for sure."

Other experts expressed similar concern.

"This is interesting, but I'm not quite sure what it means yet," said Dr. Jay Brooks, chairman of hematology/oncology at the Ochsner Health System in Baton Rouge, La. "This is a study where people recalled what X-rays they had had, and that's always a study fraught with problems," he said.

"We clearly know that there is a group of patients who are more susceptible to radiation than others," Brooks added. "This underscores the fact that doing unnecessary radiology tests should be avoided at all costs, but I still would not change the way I practice yet," he said.

Experts have long known that women who carry mutations in either the BRCA 1 or 2 genes are at increased risk (65 percent and 45 percent, respectively, by age 70) for developing breast cancer.

And several studies have shown that moderate to high doses of radiation can also increase the risk for breast cancer.

The authors of the current study speculated that BRCA carriers might be even more sensitive to radiation than other women, because BRCA proteins play a role in repairing damage to DNA, such as that caused by X-rays.

If their findings are confirmed, the authors added, women at high risk may want to use MRI or other alternatives to mammographic screening.

For now, however, there isn't enough evidence to replace the "gold standard," mammography, with breast MRI, they said.

More information

For more on breast cancer screening, visit the U.S. National Cancer Institute.