A study of 1,600 women with BRCA 1 and 2 mutations — defective genes linked to breast cancer — found they were 54 per cent more likely to suffer the disease if they had ever had a chest X-ray.

More worryingly, for women given chest X-rays before the age of 20, the risk of developing breast cancer before their 40th birthday was 2½ times greater.

The scientists said that the findings, if confirmed by further research, suggested the need for at-risk women to seek alternative methods of breast screening.

David Goldgar, who led the investigation while heading the Genetic Epidemiology Group at the International Agency for Research on Cancer in Lyons, France, said: “This is one of the first studies to demonstrate that women genetically predisposed to breast cancer may be more susceptible to low-dose ionising radiation than other women. If (the findings are) confirmed in prospective studies, young women who are members of families known to have BRCA 1 or BRCA 2 mutations may wish to consider alternatives to X-rays, such as MRI (magnetic resonance imaging).”

BRCA 1 and 2 are genes that make proteins involved in repairing damage to DNA in breast cells. X-rays disrupt DNA, but as long as the radiation dose is not too high the damage is naturally repaired. Cancer cells do not have the same self-repair ability, which is why X-rays are used in radiotherapy to destroy cancer.

“Since BRCA proteins are integral in repairing damage to breast cells, we hypothesised that women with BRCA 1/2 mutations would be less able to repair damage caused to DNA by ionising radiation,” Dr Goldgar said.

“Our findings support this hypothesis and stress the need for prospective studies.”

The researchers analysed questionnaires completed by more than 1,600 women taking part in the International BRCA 1/2 Carrier Cohort Study (IBCCS) — a major European investigation of women with BRCA mutations.

While all the women carried the mutations, not all developed breast cancer.

The women were asked whether they had ever had chest X-rays and, if so, whether it was before or after the age of 20.

The findings were published yesterday in the Journal of Clinical Oncology.

Inheriting a copy of either BRCA 1 or BRCA 2 means that a woman has an 80 per cent chance of developing breast cancer before the age of 70, as against a chance of about 10 per cent for other women.

However, only a small percentage of breast cancers are linked to the genes. Gene testing is recommended only for women with a strong family history of breast cancer — two close relatives who had the disease, or one who developed it very young.

Identifying the gene gives women the option of more frequent screening or even removal of the breasts.

Emma Pennery, nurse consultant at the charity Breast Cancer Care, said: “While excessive radiation exposure is an established risk factor for breast cancer, especially in younger people, this is one of the first studies to look at the effects of low doses . . . trials are needed to further investigate this.”

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