DNA test assesses breast cancer ‘risk score’

Scientists have been able to test how likely women are to develop breast cancer and give them a “risk score” by analysing their DNA.

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

Professor Douglas Easton, director 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.

Angelina Jolie, whose mother died of ovarian cancer, has spoken of finding out that she carries a mutation in the BRCA1 gene, which significantly increases her chances of developing both breast and ovarian cancer.

It led her to have a double mastectomy, and her ovaries and fallopian tubes were removed.

The study, which was published in the Journal of the National Cancer Institute, showed that a test for differences in 77 separate letters of DNA code could indicate a woman’s risk of developing 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 that those with a high score had a higher risk of breast cancer.

For example, a woman in the top 20% for polygenic risk score was 1.8 times more likely to develop breast cancer than the average woman.

Meanwhile, a woman in the top 1% 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 women in Europe, 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 it in their close family was 24.4% if they were in the highest-scoring fifth, compared with 8.6% 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% and 5.2%, respectively.