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.”

加拿大研究人員于本周一稱，有乳腺癌家族史的女性即使兩種易感基因的檢測結果呈陰性，患此病的幾率仍然很高。

多倫多大學的史蒂文?納羅德博士領導的研究小組稱，有乳腺癌家族史的女性患病的幾率為普通女性的4倍，也就是說她們一生中患乳腺癌的幾率約為40%。

納羅德在美國癌癥研究協會的研討會上提交了該研究成果。他說：“這一概率讓我們很吃驚，但風險如此之高，我們顯然應該采取一些預防措施。”

做胸部核磁共振檢查就是其中一項預防措施，這種針對乳腺腫瘤的檢測比乳透更為精確；服用“它莫西芬”藥物也可降低患病風險。

研究人員對1492名平均年齡為48歲的加拿大女性進行了跟蹤調查。她們攜帶的BRCA1和BRCA2兩種乳腺癌易感基因都沒有發生突變。

這些女性都有乳腺癌家族史---她們的近親中至少有兩人在50歲前患過乳腺癌，或者近親中至少有三人患過此病。

五年后，研究人員發現這些女性患乳腺癌的風險達到了普通女性的四倍。

喬治敦大學基因學專家伯斯?佩什金說：“我想，這與人們的普遍認識正好相反。易感基因檢測呈陰性還不能說明問題，家族成員有無病史才是關鍵。”