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Women with a family history of breast cancer but who test negative for two genetic mutations commonly linked to it still have a very high risk of developing the disease, Canadian researchers said on Monday.

These women are four times more likely to develop breast cancer than the average woman, translating to roughly a 40 percent lifetime risk of getting the disease, according to researchers led by Dr Steven Narod of the University of Toronto.

"I think we were surprised that it was that high. But certainly at that level of risk, one would think about preventive measures," said Narod, who presented the findings at a meeting of the American Association for Cancer Research.

Those measures may include magnetic resonance imaging, or MRI, exams of the breast, considered a more sensitive screening test for breast tumors than a mammogram, Narod said. The women also may want to consider the drug tamoxifen as a preventive measure, Narod said.

The study tracked 1,492 Canadian women with an average age of 48 who did not have mutations in either of two breast cancer susceptibility genes - BRCA1 and BRCA2.

The women came from families with a history of breast cancer - either two or more cases of breast cancer among close relatives under age 50 or at least three cases among close relatives of any age. .

After five years, those women had a fourfold higher risk than average women of developing breast cancer.

“This is contrary to what I think the common perception is,” Georgetown University genetics counselor Beth Peshkin said. “Unless a mutation is identified in the family, a negative test result doesn’t provide reassurance.”