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DNA test gives breast cancer risk

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.

Hollywood star Angelina Jolie, whose mother died of ovarian cancer, has spoken of finding 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 removed.

The study, which is 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 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 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 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.

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

Montserrat Garcia-Closas, professor of epidemiology at the Institute of Cancer Research, London, who also co-led the study, said: "Our study is the most definitive so far to show the clear benefits of using genetic testing for a large number of genetic risk factors in identifying women at elevated risk of developing breast cancer.

"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 and advice to those women most likely to benefit from them.

"It's now important to work out how this sort of test could be used widely in a healthcare, rather than in a research setting. Currently available tests can analyse a handful of high-risk genes, but outside of looking for changes to these genes in women with a history of breast cancer in their close family, genetic testing is not widely offered to women."

Nell Barrie, senior science communications manager at 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."

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