Women genetically predisposed to breast cancer were found to be even more likely to develop the condition if they were exposed to low-dose ionising radiation from chest X-rays.
The finding supports the use of MRI scans in place of conventional mammography for potential carriers of the BRAC1 or BRAC2 mutation, the researchers said.
The study included 1,601 women who were known carriers of the BRAC1 or BRAC2 gene mutation.
Using questionnaire data, the researchers looked for any relationship between chest X-ray exposure and cancer incidence in this high-risk group. They found women with the BRAC1 or 2 mutation who were exposed to chest X-rays at any age had a 54 per cent increased risk of developing breast cancer.
Those exposed to chest X-rays before the age of 20 were 2.5 times as likely to develop breast cancer before the age of 40 as those not exposed.
Lead researcher Dr David Goldgar, head of the genetic epidemiology group at the International Agency for Research on Cancer in Lyon at the time the research was conducted, said: 'Since BRCA proteins are integral in repairing damage to breast cells, we hypothesised that women with BRCA 1 or 2 mutations would be less able to repair damage caused to DNA by ionizing radiation. Our findings support this hypothesis.
'This is one of the first studies to demonstrate that women genetically predisposed to breast cancer may be more susceptible to low-dose ionizing radiation than other women.
'Young women who are members of families known to have BRCA1 or BRCA2 mutations may wish to consider alternatives to X-ray, such as MRI.'
- Journal of Clinical Oncology online