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.”

加拿大研究人员于本周一称，有乳腺癌家族史的女性即使两种易感基因的检测结果呈阴性，患此病的几率仍然很高。

多伦多大学的史蒂文?纳罗德博士领导的研究小组称，有乳腺癌家族史的女性患病的几率为普通女性的4倍，也就是说她们一生中患乳腺癌的几率约为40%。

纳罗德在美国癌症研究协会的研讨会上提交了该研究成果。他说：“这一概率让我们很吃惊，但风险如此之高，我们显然应该采取一些预防措施。”

做胸部核磁共振检查就是其中一项预防措施，这种针对乳腺肿瘤的检测比乳透更为精确；服用“它莫西芬”药物也可降低患病风险。

研究人员对1492名平均年龄为48岁的加拿大女性进行了跟踪调查。她们携带的BRCA1和BRCA2两种乳腺癌易感基因都没有发生突变。

这些女性都有乳腺癌家族史---她们的近亲中至少有两人在50岁前患过乳腺癌，或者近亲中至少有三人患过此病。

五年后，研究人员发现这些女性患乳腺癌的风险达到了普通女性的四倍。

乔治敦大学基因学专家伯斯?佩什金说：“我想，这与人们的普遍认识正好相反。易感基因检测呈阴性还不能说明问题，家族成员有无病史才是关键。”