Scientists have identified a genetic defect which can increase the risk of ovarian cancer by 40%.
A variant of the genetic code has been located on the ninth chromosome by British researchers who analysed the DNA of nearly 2,000 women with ovarian cancer and 2,500 women without the disease.
Around 15% of women across the UK are believed to be carrying a pair of the variant in their DNA, increasing their one in 100 lifetime risk of developing ovarian cancer by 40%.
Researchers estimate that around one in five women have one copy of the defective code, raising their risk levels by 20%
Two breast cancer genes - BRCA1 and BRCA2 - are already known to be associated with the disease, but they are rare and possibly account for less than 5% of all ovarian cancer cases.
Cambridge University professor and study leader, Dr Paul Pharoah, said: "It is likely that the remaining risk is due to a combination of several unidentified genes - which individually carry a low to moderate risk. Now we have ticked one off, the hunt is on to find the rest."
The findings from the eight-year study are published in the journal Nature Genetics.