Women with a strong family history of breast cancer are four times more likely than average to develop the disease even without a high-risk gene, scientist have learned.

For the first time, researchers have evaluated the risk for women who do not have a faulty BRCA gene but have close relatives with breast cancer.Women who inherit a defective BRCA1 or BRCA2 gene have an 80% chance of developing breast cancer in their lifetime. They are also likely to become ill at a younger age than usual.

But experts know there are other genes linked to the disease which also run in families.A team of Canadian-led scientists looked at women with one first-degree relative under 50 with breast cancer and at least one other relative with the disease, or three relatives of any age.

Despite not having a faulty BRCA gene, just over one in three of the women developed breast cancer compared with an average rate for the general population of one in nine.A significant family history of breast cancer alone could be strong enough grounds for doctors to offer preventative treatments, say the researchers.

Study leader Dr Steven Narod, from the University of Toronto, said: "Although the risk of breast cancer for this group of women - those with a family history of the disease but who don't carry a faulty BRCA gene - is not as high as those who do carry the gene, it is still significant enough for doctors to start thinking about appropriate preventative treatments to stop women developing the disease.

"This is the first time the breast cancer risk for this group of women has been measured, and it's significantly higher than that of the general population."It's important to start thinking about action to prevent breast cancer in women who are at high risk of developing the disease."