Over 4,000 UK women die from ovarian cancer each year
Scientists have identified a genetic flaw which can increase the risk of ovarian cancer.
The international team of researchers, led by UK scientists, looked at the DNA of 17,000 women for their study.
In Nature Genetics, they said carrying two copies of the flaw increased the chance of cancer by 40% - around 15% of UK women have both copies.
Cancer experts said it was an important discovery which could help manage women who were at increased risk.
Ovarian cancer is the fifth most common cancer in women in the UK with around 6,800 new cases diagnosed each year in the UK.
This leads to around 4,300 deaths each year.
The BRCA1 and BRCA2 genes, which cause breast cancer are already known to significantly increase the risk of ovarian cancer - but faults in these genes are rare and probably cause fewer than 5% of cases so scientists have been looking for other genetic faults which could help explain inherited risk.
The researchers, led by scientists based at the Cancer Research UK Genetic Epidemiology Unit at the University of Cambridge and University College London (UCL), searched through the genomes of 1,810 women with ovarian cancer and 2,535 women without the disease from across the UK.
It is the fifth most common cancer in UK women, affecting 6,800 women per year
Five out of every 100 cancers diagnosed in women are ovarian
A family history of the cancer, breast cancer and being infertile or having fertility treatment, are all known to increase risk
They analysed 2.5m variations in the genetic code and found genetic "letters" - called single nucleotide polymorphisms (SNPs) - which when spelt slightly differently increase ovarian cancer risk in some women.
It is the first time scientists have found a SNP linked uniquely to risk of ovarian cancer.
Everyone has 23 pairs of chromosomes, with one of each pair inherited from each parent.
This SNP is located on chromosome nine.
The risk of developing ovarian cancer for women carrying the variation on both chromosomes is 14 in 1,000, compared with 10 in 1,000 for those who do not.
Carrying one flawed variant increases the risk to 12 in 1,000.
Scientists confirmed their finding after working with the international Ovarian Cancer Association Consortium and examining more than 7,000 more women with ovarian cancer and 10,000 women without disease.
'Laying the groundwork'
Dr Simon Gayther from UCL, who worked on the study, said: "There is now a genuine hope that as we find more genetic variants, we can start to identify the women at greatest risk and this could help doctors to diagnose the disease earlier when treatment has a better chance of being successful."
Dr Andrew Berchuck, head of the international Ovarian Cancer Association Consortium steering committee, said: "This study confirms that ovarian cancer risk is partly determined by genetic variants present in a large number of women.
"This initial discovery and others that will likely follow in the future lay the groundwork for individualised early detection and prevention approaches to reduce deaths from ovarian cancer."
Dr Lesley Walker, director of cancer information at Cancer Research UK, added: "This is an important discovery.
"This research paves the way for scientists to discover even more genes linked to ovarian cancer and could lead to new approaches to treat or prevent the disease. Crucially it will help doctors manage women who are at increased risk."