Genetic test analyses 77 genes for breast cancer risk

A new wide-ranging test that looks at multiple sites in the DNA code could help predict a woman's risk of developing breast cancer.

A research team, led by scientists at the University of Cambridge and the Institute of Cancer Research, looked at 77 genetic sites that have been identified as influencing a woman's chance of developing breast cancer. 

These 77 genes have previously been identified as 'risk sites' - individually they have a low impact on cancer risk, but in combination they have a much more powerful effect. Through analysis of these sites, scientists have been able to calculate an individual's risk of developing breast cancer. 

Studying the genomes of 65,000 women, researchers devised a 'polygenic risk score' (PRS) based on the appearance of faults in each of these 77 genes. Using data from one of the world's biggest genetic information stores, the Collaborative Oncological Gene-environment Study (COGS), the researchers were able to find links between these genetic faults and a woman's risk of developing breast cancer. The research was published in the Journal of the National Cancer Institute.

A woman with a PRS in the top one percent was around three times more likely to develop breast cancer than average. Among women with no family history of breast cancer, those in the highest-scoring fifth had a 16.6 percent chance of developing breast cancer, whereas those in the lowest-scoring fifth had just a 5.2 percent chance of developing the disease. 

Nell Barrie, senior science communications manager at Cancer Research UK, 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.'

One of the study's leaders, Professor Douglas Easton from 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.'

Research into other genetic markers for breast cancer is underway globally. Australian scientists recently published work on a DNA-binding protein called Inhibitor of Differentiation 4 (ID4). High levels of ID4 in mice seem to be associated with the most aggressive form of the disease - so-called 'triple negative' breast cancer - and this work has shown that blocking ID4 stops breast-cancer cells from dividing. They hope that drugs could be developed to block this protein in humans, leading to treatments for this resistant form of breast cancer.