Five new genetic variants have been discovered which, in combination, raise the risk of developing breast cancer by 16 per cent, according to a new study in Nature Genetics.
Scientists compared DNA samples from 3,659 women with breast cancer and a family history of the disease, against DNA from 4,897 unaffected controls. The study found that 1.2 per cent of familial breast cancer risk can be explained by these five new variants located on chromosomes nine, 10 and 11. Gene variants previously linked to breast cancer, including BRCA1 and BRCA2, were also found to increase risk.
Lead author of the study, Dr Douglas Easton, said: 'We know for sure that these gene variations are associated with risk. It is not the whole picture but it will contribute ultimately to genetic profiling of risk. It also contributes to our understanding of why the disease develops and will lead to a better understanding of the biology of the disease'.
Dr Helen George, head of science information at Cancer Research UK, said: 'This is by far the largest study of its kind to explore the common genetic variations that contribute to breast cancer risk. This research takes us a step closer to developing a powerful genetic test for the disease. Such a test could help doctors identify women who have an increased risk so that they can make informed decisions about how to take steps to reduce their chance of developing the disease'.
There are now 18 common genetic variations known to be linked to a small increased family risk of breast cancer, according to the study. These variations are thought to account for around eight per cent of inherited cases of breast cancer. Rarer mutations, which are known to confer a high and moderate risk of breast cancer, explain a further 20 per cent of familial risk.
The genetics of breast cancer are complex and further studies are required to determine what other genetic factors contribute to risk, according to NHS Choices.
The NHS says having these variants does not mean a person will definitely develop the disease, only that their likelihood is increased. Additional significant risk factors include age and post-menopausal obesity.
Almost 46,000 women and 300 men are diagnosed with breast cancer each year in the UK, according to the charity Breakthrough Breast Cancer.
The research was conducted at the Institute of Cancer Research in Surrey and additional institutions within the UK and the Netherlands.