A new blood test may offer women an early warning of breast cancer even if they do not inherit genes associated with the disease.
Researchers have identified a molecular “switch” in blood samples that increases chances of having breast cancer.
The marker is associated with the BRCA1 breast cancer gene, but was also found in those without the mutation who went on to develop the disease.
Around 10% of breast cancers are caused by BRCA1 and BRCA2 gene variants inherited from parents.
A woman with the BRCA1 gene has an 85% risk of developing breast cancer, leading some carriers to take the step of breast removal.
This leaves around 90% of cases unexplained and until now there has been no reliable way of predicting the likelihood of non-inherited breast cancer.
The “switch” is part of the process by which certain molecules acting on DNA cause genes to be turned on or off.
Professor Martin Widschwendter, from University College London, said: “We identified an epigenetic signature in women with a mutated BRCA1 gene that was linked to increased cancer risk and lower survival rates.
“Surprisingly, we found the same signature in large cohorts of women without the BRCA1 mutation and it was able to predict breast cancer risk several years before diagnosis.
“The data is encouraging since it shows the potential of a blood-based epigenetic test to identify breast cancer risk in women without known predisposing genetic mutations.”
Dr Matthew Lam, senior research officer at the charity Breakthrough Breast Cancer, described the findings as “definitely promising”.
He added: “This could mean that in the future a woman may be able to have a simple blood test to look for this DNA signature, and therefore know if she is at a higher risk of developing breast cancer.
“If she does have this signature, she could then work with her doctor to explore the options available to help her take control of her own risk.
“These could include lifestyle changes, tailored breast screening, risk-reducing drugs or surgery.”
Their results appear in the online journal Genome Medicine.