X-rays are a form of ionizing radiation
Chest X-rays may increase the chances of breast cancer in women with high risk genes, research suggests.
An analysis of 1,600 women with high risk BRCA1 and 2 gene mutations suggested exposure to low-level X-rays did have an effect.
The study found exposure before the age of 20 may be linked to particularly heightened risk.
The Journal of Clinical Oncology study was led by the International Agency for Research on Cancer in France.
Women who inherit a damaged BRCA1 gene have a 60-85% chance of developing breast cancer
They also have a 20-40% chance of developing ovarian cancer
For BRCA2, the risks are 40-60% and 10-20% respectively
Around 1 in 1,000 women in the UK carry a damaged version of the BRCA1 gene and 1 in 700 carry a faulty BRCA2 gene
Lead researcher Dr David Goldgar said: "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.
"If confirmed in prospective studies, 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."
The researchers found that women with BRCA1 and 2 mutations who had undergone a chest X-ray were 54% more likely to develop breast cancer than women who had never undergone the procedure.
Women who were exposed to X-rays before age 20 had a 2.5-fold increased risk of developing the disease before age 40, compared with women who had never been exposed.
Dr Goldgar said BRCA proteins played a key role in repairing damage in breast cells.
Thus, women carrying mutated versions of the genes which control their production may be less able to repair any damage associated with exposure to the ionizing radiation emitted by X-rays.
However, the researchers admitted that it was possible that women who had gone on to develop breast cancer might be more likely to remember having had an X-ray than those who remained free from the disease.
They also failed to collect data on the specific dose and timing of radiation that was received.
Dr Laura-Jane Armstrong, of the charity Cancer Research UK, said: "Although interesting, the results of this study are not conclusive.
"Women who carry faulty BRCA genes have an increased risk of developing breast cancer, but more research is needed to confirm whether or not chest X-rays increase breast cancer risk in women with faults in the BRCA genes."
Dr Emma Pennery, of the charity Breast Cancer Care, said excessive radiation exposure was an established risk factor for breast cancer - but there was little research into the effect of lower doses.
"It is important to remember that 90% of breast cancer cases are not hereditary and that most healthy women would not need to have frequent chest X-rays, especially if in their twenties."
Dr Sarah Rawlings, of Breakthrough Breast Cancer, said around 5% of the 41,000 breast cancers diagnosed in the UK each year were linked to BRCA1 and BRCA2 mutations.
"As this group of women are already at high risk of developing breast cancer any information on factors which may alter their risk is important. However this study does not yet offer conclusive evidence.
"It's still important for women to attend their breast screening appointments as mammography can detect breast cancer early when it is more likely to be successfully treated. Anyone with concerns should talk to their doctor."
Arlene Wilkie, of the Breast Cancer Campaign said: "Before any advice can be given to those carrying mutations in their BRCA1 and 2 genes a study designed to follow participants forward in time, rather than retrospectively, is needed."