The study cannot prove a link between the radiation and breast cancer, but it is one of the biggest ever to look at the issue. The research was published Thursday in the journal BMJ.
"This will raise questions and caution flags about how we treat women with mutations," said Len Lichtenfeld, deputy chief medical officer of the American Cancer Society. He and the society had no role in the research.
Mammograms are most often used in women over 40, unless they are at high risk, such as carrying a mutation of the BRCA1 or BRCA2 gene. Having such a mutation raises the risk of developing cancer fivefold. About one in 400 women has the gene abnormalities, which are more common in Eastern European Jewish populations. Unlike mammograms, an MRI, or magnetic resonance imaging scan, doesn't involve radiation.
The screening tests have been proven to save lives and are clearly beneficial for women aged 50 and over who have an average risk of breast cancer. Experts are divided on their value in women under 50.
Some studies have suggested women with the genetic mutations could be more sensitive to radiation because the genes are involved in fixing DNA problems. If those genes are damaged by radiation, they might not be able to repair DNA properly, raising the cancer risk.
In several European countries, doctors already advise women with BRCA mutations to get MRIs instead of mammograms before age 30. In the United States, there is no specific advice from a leading task force of government advisers, but the American Cancer Society recommends yearly mammograms and MRIs from age 30 for women with BRCA gene mutations.
In the BMJ study, European researchers followed nearly 2,000 women over age 18 with one of the gene mutations in Britain, France, and the Netherlands. Participants reported their previous chest X-rays and mammograms, including the age of their first screening and the number of procedures. About 850 women were later diagnosed with breast cancer. Roughly half of them had X-rays, while one-third had at least one mammogram, at an average age of 29.
Researchers found women with a history of chest radiation in their 20s had a 43 percent increased relative risk of breast cancer compared with women who had no chest radiation at that age. Any exposure before age 20 seemed to raise the risk by 62 percent. Radiation after age 30 did not seem to affect breast cancer risk.
The study was paid for by European cancer groups.
Lichtenfeld said women who need scans involving radiation shouldn't avoid them because of breast cancer fears.