A team of Canadian-led scientists evaluated the risk for women who do not have a faulty BRCA gene developing breast cancer but have close relatives with the disease.
The results showed they were four times more likely to develop the condition even without the defective BRCA1 or BRCA2 gene, which itself is associated with an 80% chance of developing breast cancer.
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, one in three of the women developed breast cancer compared with an average rate for the general population of one in nine.
Identifying women with a family history of breast cancer could lead to preventative treatments such as courses of tamoxifen being offered to those at greatest risk. However, tamoxifen is not currently licensed for this use in the UK
Study leader Dr Steven Narod, from the University of Toronto, said: 'It's important to start thinking about action to prevent breast cancer in women who are at high risk of developing the disease.'