WASHINGTON (Reuters) - 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," Narod, who presented the findings at a meeting of the American Association for Cancer Research, said in a telephone interview.
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 involved 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. Narod said it had been unclear exactly what risk breast cancer posed to women in these circumstances.
Most women who get genetic testing for the BRCA1 and BRCA2 are not found to have these abnormalities.
While BRCA1 and BRCA2 mutations also are associated with a higher risk for ovarian cancer, the women in this study did not have a greater likelihood for that ailment.
Narod said the lifetime risk of breast cancer estimated for these women compared to the roughly 80 percent lifetime risk for women with the BRCA1 or BRCA2 mutations.
The likelihood that a woman's breast cancer is linked to the BRCA1 and BRCA2 genes is particularly high among women with an Ashkenazi, or Eastern European, Jewish background.
Each year, breast cancer kills about 465,000 women worldwide and 1.3 million develop it, according to the American Cancer Society.
Editing by Bill Trott