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Nov. 17, 2008 -- Women with a strong family history of breast cancer who do not have genes associated with increased risk of the disease have a fourfold greater chance of developing it than the average woman, new research indicates.
The finding may help doctors detect breast cancer earlier in high-risk women and lead to more and earlier preventive treatments, says the University of Toronto's Steven Narod, MD, senior author of the study.
Women with several blood relatives who have breast cancer have been known for years to be at higher risk themselves, Narod tells WebMD.
"We've always considered two groups of women -- those with family history of breast cancer and those with BRCA1 and BRCA2 genes -- to be at higher risk," Narod says. "But no one has ever looked at those with high risk of cancer because of family history, but negative tests [for BRCA1 and BRCA2]. It was assumed that most of the risk could be explained by those mutations."
The findings suggest that additional genes, hormones, or other unknown factors, perhaps environmental, are also responsible for causing breast cancer, Narod says.
That seems apparent from the study's finding that women with a strong family history were still at higher risk for developing the disease even if they didn't have BRCA gene mutations, Narod says.
"Now when we see families such as this, we will be able to offer better advice about their actual risk," he says. "It is clear to me that the risk is high enough that we need to discuss options, such as breast MRI for screening and chemoprevention with tamoxifen or raloxifene. Our hope is to be able to prevent or pick up on breast cancer early enough to stop patients from dying."
Kelly Metcalfe, RN, PhD, also of the University of Toronto, tells WebMD that "only 5% of women with breast cancer have a BRCA mutation," and therefore "it has been difficult to counsel women without a mutation" about their breast cancer risk.
"For a woman in which we do find a mutation, she has an approximate 80% risk of developing breast cancer," Metcalfe says. "For women with a significant family history of breast cancer, without a BRCA1-2 mutation, we can now say that she has an approximate 40% risk of developing breast cancer. This can be compared to a 10% risk of breast cancer for a woman in the general population."
The "take-away" message from the research, in which 1,492 women with first-degree breast cancer relatives were studied, is this, Metcalfe says:
"Having a BRCA mutation is the greatest risk factor for developing breast cancer. However, we still need to be very aware of a woman's family history of breast cancer, even without a mutation."