Existing figures already indicate that 2% of breast cancers arise because of mutations in BRCA1 and BRCA2 genes, and women with these faulty genes have a 45 to 65% higher risk of developing breast cancer than women who don't have them.
What the new study shows is women with this genetic risk who are exposed to chest X rays before the age of 30, have a 43% higher risk over and above that, compared to equivalent women with the same genetic risk who are not exposed to chest X rays before that age.
BRCA genes are important for repairing damage to DNA, which can lead to cancer. Radiation like X rays damage DNA. Thus women with faulty BRCA are less able to repair the damage caused by radiation, which puts them at greater risk for developing breast cancer.
Study author Douglas Easton, a Cancer Research UK scientist at the University of Cambridge, told the press "it is important that these women and their doctors are aware of this".
The Study Examined Nearly 2,000 Women with Faulty BRCA GenesFor their study, Easton and colleagues examined data on 1,993 women with mutations in BRCA1 and BRCA2 genes recruited between 2006 and 2009 to take part in studies in the Netherlands (HEBON), France (GENEPSO), and the UK (EMBRACE).
The data shows 848 (43%) of the women were diagnosed with breast cancer, 926 (48%) reported ever having an X ray, and 637 (33%) a mammogram. The average age at first mammogram was 29.
Easton and colleagues found that any X ray exposure to the chest area between the age of 20 and 29 raised the risk of breast cancer by 43%. And any exposure before the age of 20, raised it by 62%. But for exposures occurring between 30 and 39, there appeared to be no raised risk of breast cancer.
Looking at the results a different way, current estimates suggest out of 100 women with the BRCA1/2 mutation aged 30, nine will develop breast cancer by the age of 40, but the findings from this study suggest the nine rises to 14 if all 100 have one mammogram before the age of 30.
Results Should Be Interpreted with CautionHowever, the researchers say people should be cautious when using this estimate, because of the low numbers: among the participants only a few with breast cancer had had a mammogram before the age of 30.
They also say they were "puzzled" by some of the differences in breast cancer risk for BRCA1 and BRCA2 carriers, and call for larger studies to find out if these really exist.
But they do recommend doctors use non-ionizing imaging techniques, such as MRI, with BRCA1 and BRCA2 carriers.
Such a policy is already in place in the UK.
Written by Catharine Paddock PhD