A genetic test could help predict breast cancer many years before it develops, scientists claim.
Their study shows the risk can double in women whose genes have been changed by exposure to environmental factors such as hormones, radiation, alcohol, smoking and pollution.
The findings could lead to a blood test that will identify those most at risk of breast cancer and other forms of the disease, the researchers say.
Breakthrough? The findings of a new study suggest that women whose genes have been altered by environmental factors carry double the risk of developing breast cancer
In the study, blood samples were taken from 1,380 women of various ages who had not developed breast cancer.
The researchers investigated whether the alteration of a single gene by a process called methylation can predict whether women are at more risk of breast cancer.
Women showing the highest methylation levels affecting a white blood cell gene called ATM were twice as likely to develop breast cancer as those with the lowest levels.
Methylation is a reprogramming mechanism that allows genes to be affected by exposure to environmental factors.
Such effects are being seen as important drivers of cancer and they can occur in the womb, around birth or later.
Altogether, 640 women in the study developed cancer and on average the blood tests were carried out three years before diagnosis.
In some cases the results pre-dated the discovery of breast cancer by up to 11 years. The results were especially clear in blood samples from women under the age of 60.
Human breast cancer cells dividing: A woman has a one in nine chance of developing the disease
The average risk of developing breast cancer is one in nine over a woman’s lifetime. James Flanagan, of Imperial College London, who led the research, said: ‘We know that genetic variation contributes to a person’s risk of disease.
‘With this new study we can now also say that epigenetic variation, or differences in how genes are modified, also has a role.
‘We hope this research is just the beginning of our understanding about the epigenetic component of breast cancer risk.
‘The challenge will be how to incorporate all of this new information into the computer models that are currently used for individual risk prediction.’
He said the study raised the possibility of a simple blood test to assess breast cancer risk in advance by looking at alteration on individual genes.
Combined with other information, such as a family history of breast cancer, it could help identify women who might benefit from monitoring or pre-emptive action involving surgery or preventive drugs.
The research, funded by the Breast Cancer Campaign, was published in the journal Cancer Research.
Baroness Delyth Morgan of Breast Cancer Campaign said: ‘Dr Flanagan’s research into epigenetics is so exciting because it suggests that there is every possibility the risk of developing breast cancer could be decided many decades in advance.
‘By piecing together how this happens, we can look at ways of preventing the disease and detecting it earlier to give people the best possible chance of survival.’
The ATM gene has been linked to other cancers, including lymphoma and leukaemia.
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