Carriers of certain gene mutations are at greater risk of developing breast cancer if exposed to chest X-rays, research has shown.
Women with faults in either BRCA1 or BRCA2 genes are more vulnerable to the disease than the general population.
And the international study, part-funded by Cancer Research UK, found exposure to ionising radiation in childhood and adolescence further increased the probability of suffers getting the cancer.
The research of 2,000 women said 2% of breast cancers were caused by BRCA faults and that women with the condition had a 45% to 65% chance of developing the disease.
Study author Professor Douglas Easton, a Cancer Research UK scientist at the University of Cambridge, said: "BRCA genes help repair DNA damage - damage which can be caused by exposure to radiation like X-rays.
"Women with faults in these genes are less able to repair damage caused by radiation, so they are at a greater risk of developing breast cancer."
Patients 30 years old and above in the UK are now screened for breast cancer using magnetic resonance imaging (MRI) with no exposure to radiation.
Dr Julie Sharp, senior science information manager at Cancer Research UK, said the research highlighted that the procedure provided better protection for younger women.
The study was carried out in association with The Institute of Cancer Research, The Royal Marsden NHS Foundation Trust, St Mary's Hospital and Addenbrokes Hospital.
Subject to approval
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