DNA test shows breast cancer risk

Researchers said that improving the accuracy of risk analysis using genetic screening could help breast cancer prevention and save lives.

Professor Douglas Easton, of the Centre for Cancer Genetic Epidemiology at the University of Cambridge, who co-led the study, said he hoped genetic risk prediction will become part of routine breast screening in future.

Currently only women with a family history of breast cancer are referred for genetic screening.

Hollywood star Angelina Jolie, whose mother died of ovarian cancer, has spoken of finding she carries a mutation in the BRCA1 gene, which increases her chances of developing both breast and ovarian cancer. It led her to have a double mastectomy, and her ovaries and fallopian tubes removed.

The study, published in the Journal of the National Cancer Institute, showed that a test for differences in 77 letters of DNA code could indicate a woman’s risk of breast cancer, in women with or without a family history of the disease.

Researchers came up with a “polygenic risk score” for each woman based on their DNA code, and found those with a high score had a higher risk of breast cancer. For example, 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. Meanwhile, a woman in the top one per cent for the polygenic risk score was three times more likely to develop breast cancer than average – corresponding to a risk for these women of around one in three.

The research, which looked at 65,000 European women, found that analysing this panel of 77 genetic markers was much more accurate in defining risk than previous tests that used fewer markers.

Lifetime risk of breast cancer for women with a history of the disease 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.

However, for women without a history of breast cancer in their close family, the risks were 16.6 per cent and 5.2 per cent respectively.

Montserrat Garcia-Closas, of the Institute of Cancer Research, London, said: “This type of testing could fit alongside other standard risk measures, such as family history and body mass index, to improve our ability to target the best preventive treatments.”

Nell Barrie, of Cancer Research UK, which helped fund the research, 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.”