Genetic testing for breast cancer could be expanded after four new risk genes were identified by scientists.
Inheriting certain mutations increases the odds of being struck by the disease.
A typical 15% risk rises to 60-90% for those carrying an altered BRCA1 gene and 45-85% for those with a BRCA2 fault.
Hollywood star Angelina Jolie famously had a double mastectomy after being told she carried the BRCA1 mutation and had an 87% risk of breast cancer.
Tests can check for a few known faults but not all the genetic risks.
Researchers at Cambridge University and in Canada analysed data from 26,000 women with breast cancer and 217,000 others without. They found four novel genes that appeared to increase risk of the disease.
Professor Jacques Simard, from Université Laval in Quebec, said although most of the variants identified were rare, the risks could be significant for women who carried them.
He added: “For example, alterations in one of the new genes, MAP3K1, appear to give rise to a particularly high risk of breast cancer.”
Prof Douglas Easton, of Cambridge University, said more research was needed, including the role of “lifestyle factors”.
Around 55,000 women are diagnosed with breast cancer every year in the UK.
Dr Kotryna Temcinaite, at Breast Cancer Now, welcomed the “exciting research” and said it could open the door to new treatment and support.
The findings were published in the journal Nature Genetics.
