LONDON — Mammograms aimed at finding breast cancer might raise the chances of developing it in young women whose genes put them at higher risk for the disease, a study by European cancer agencies suggests.

The added radiation from mammograms and other types of tests with chest radiation might be especially harmful to them, and an MRI is probably a safer way of screening women younger than 30 who are at high risk because of gene mutations, the authors conclude.

The study doesn't prove a link between the radiation and breast cancer, but it is one of the biggest 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 (gene) mutations," said Dr. 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 older than 40, unless they are at high risk; such women include those who carry a mutation of the BRCA1 or BRCA2 gene. Having such a mutation increases 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, does not involve radiation.

The breast-cancer screening tests have been proven to save lives and are clearly beneficial for women 50 and older who have an average risk of breast cancer. Experts are divided about their value in women younger than 50.

In several European countries including Britain, the Netherlands and Spain, doctors already advise women with BRCA mutations to get MRIs instead of mammograms before age 30. In the U.S., 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 older than 18 with one of the gene mutations in Britain, France and the Netherlands. About 850 women were later diagnosed with breast cancer. 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.