A single genetic fault in a gene that normally helps the body to repair its DNA increases a woman's risk of ovarian cancer six-fold, a study has found.
One in every 11 women who carry the faulty gene is likely to develop ovarian cancer at some point in her life compared with a typical risk of about one in 70 for women in the general population, scientists said.
Cancer Research UK, the cancer charity that funded the study, said that the landmark discovery by British scientists is the most important breakthrough in understanding the genetics of ovarian cancer for more than a decade.
The research involved analysing the genomes of more than 900 families affected by hereditary breast and ovarian cancer to see if they carry any genetic faults that could account for their higher risk of developing the disease compared with the general population.
About 6500 women in the UK are diagnosed with ovarian cancer each year - the fifth-most-common cancer - and the scientists estimated that between 40 and 50 of these women are likely to carry faults in a DNA-repair gene known as RAD51D.
It is known that RAD51D is one of a number of genes that is involved with repairing DNA when it is damaged by, for instance, chemicals in the environment.
If RAD51D is itself damaged, then it cannot repair DNA mutations that can lead to the cell becoming cancerous.
"Women with a fault in RAD51D gene have a one in 11 chance of developing ovarian cancer. At this level of risk, women may wish to consider having their ovaries removed after having children to prevent ovarian cancer occurring," said Professor Nazneen Rahman of the Institute of Cancer Research in London.
The study, published in the journal Nature Genetics, suggests that drugs known as Parp inhibitors which were originally designed to treat breast, ovarian and prostate cancers triggered by faults in another gene, called BRCA1, may also be effective against RAD51D faults.
"There is also real hope on the horizon that drugs specifically targeted to the gene will be available," said Professor Rahman.
Scientists hope to develop a test for the faulty gene which can be used to identify patients who would benefit from such drugs.
Harpal Kumar, chief executive of Cancer Research UK, said: "Survival from ovarian cancer has almost doubled in the last 30 years. This landmark discovery is another piece of the jigsaw deepening our understanding of the disease. We hope this will have a significant impact in providing more personalised treatments for patients based on their genetic make-up, saving more lives from ovarian cancer."
Louise Bayne, chief executive of the ovarian cancer charity Ovacome, said: "This new discovery is greatly welcomed by the ovarian cancer community, as it helps to unravel a little more of the complicated ovarian cancer story and offers hope for better treatments in the future."