New breast cancer risk test devised

The team analysed 77 separate letters of DNA code, discovering that they had a low impact of cancer risk individually, but together formed a powerful combination. The tests look for changes and mutations in the BRCA genes - which can give women a 90 per cent chance of cancer at some point in her lifetime.

The research led by the Institute of Cancer Research and the University of Cambridge, studied more than 65,00 women and looked at the subtle changes in a woman's genetic code, which if not treated will influence the chances of developing cancer. Of the 77 cancer-risk sites in the DNA inherited from the mother and the 77 cancer-risk sites from the father, an average woman will gain 66.

They found a significant link between the score – called a ‘polygenic risk score’ – and a woman’s breast cancer risk. A woman in the top 20 per cent for polygenic risk score was 1.8 times more likely to develop breast cancer than the average woman. A woman in the top one per cent for the polygenic risk score was more than three times more likely to develop breast cancer than average – corresponding to a risk for these women of around one in three.

Lifetime risk of breast cancer for women with a history of breast cancer in their close family was 24.4 per cent if they were in the highest-scoring fifth – compared with 8.6 per cent if they were in the lowest fifth. But for women without a history of breast cancer in their close family, the risks were 16.6 and 5.2 per cent respectively.

Professor Montserrat Garcia-Closas said: "I think it's very exciting at the moment. The discovery of these variants has progressed very quickly in the last five years and I think it's reaching a plateau. And at that point it's time to start designing a genetic test that includes all these elements. That's likely to be reached within a year."

The ability to accurately predict the risk of breast cancer could have a powerful impact on medicine, as it could more clearly show which women need drugs to reduce the risks. Those within the field know that, despite the possible influence this could have, there remains a difficulty in combining these tests with current techniques.

Professor Douglas Easton, of the University of Cambridge, said: "There's still work to be done to determine how tests like this could complement other risk factors, such as age, lifestyle and family history, but it's a major step in the right direction that will hopefully see genetic risk prediction become part of routine breast screening in the years to come."

Cancer Research UK's Nell Barrie said: "This study shows how the genetic map of breast cancer that scientists have been building up over the years might be used to identify women most at risk, so we can take steps to reduce their chances of developing the disease or catch it at the earliest possible stage."

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