The research team believe the test could reduce the number of women opting for pre-emptive mastectomy by as much as one-third in those with a BRCA mutation, and give breast cancer patients the chance to make more informed decisions.
'With more accurate genetic testing, we can better predict a woman's risk of developing the disease and therefore offer the appropriate advice and support, rather than a "one size fits all" approach,' said Lester Barr, chairman of Prevent Breast Cancer, a UK charity based in Manchester which part-funded the research.
The new test assesses an individual's risk of developing breast cancer by analysing genetic variations at 18 positions within their DNA code. These variants are known as SNP (single nucleotide polymorphism) and have been shown to be indicative of breast cancer risk in women who do not carry BRCA mutations. While they showed minimal effects individually, when data on the SNPs was combined together, it affected a person's risk considerably.
The case-control study group consisted of 451 women with a family history of breast cancer, who had also developed breast cancer. Of these, 112 carried BRCA mutations. The researchers compared genetic profiles of these women against a control group of 1605 women (691 of whom carried BRCA mutations).
Researchers also took into account other factors when calculating risk, including age at first assessment, height and weight, and family history of breast cancer.
Many women who had previously been classified as high risk (with a 30 percent chance or higher of developing the disease during their lifetimes) were reclassified as lower risk, a group in which mastectomy is not recommended.
The predictions devised during this research have been confirmed by Prevent Breast Cancer's 'Predicting Risk of Cancer at Screening' (PROCAS) study, in which 10,000 women underwent SNP testing, and 455 then went on to be diagnosed with breast cancer.
Initially this new test will only be available at St Mary's and Wythenshawe hospitals in Manchester, however Prevent Breast Cancer is hopeful this will be available to the whole population 'in the next one to two years'.
'This new test will help women at risk of familial breast cancer to make more informed decisions about their care,' said Professor Gareth Evans, at the University of Manchester and St Mary's Hospital, who led the study.
'BRCA1 and BRCA2 are just part of what we should be looking for when assessing risk and in Manchester we plan to incorporate screening for these new genetic markers in clinical practice within the next six months,' he added.