A team at Imperial college London says it's the "first strong evidence" that the molecular changes, which can switch genes on and off, set the stage for breast cancer many years before it is diagnosed.
Dr James Flanagan, who led the team, said it raised the possibility of a blood test to assess risk at a very early stage, thus revolutionise the treatment for the disease, the 'Daily Express' reported.
Combined with other information, such as a family history of breast cancer, it could help identify women who might benefit from pre-emptive action.
In their research, the scientists analysed blood samples from 1,380 women of various ages, 640 of whom later developed breast cancer. A strong link was found between the molecular modification of a white blood cell gene, called ATM, and breast cancer risk.
In fact, they looked for evidence of a chemical effect called methylation which acts as a "gene switch".
Women showing the highest methylation levels affecting the ATM gene were twice as likely to develop breast cancer as those with the lowest levels. (MORE) PTI MOT MOT
