Most inherited cases of breast cancer are associated with one of two abnormal genes: BRCA1 (BReast CAncer gene one) or BRCA2 (BReast CAncer gene two).
Women with a BRCA1 or BRCA2 genetic mutation:
- have up to a 72% lifetime risk of developing breast cancer
- have a much higher-than-average lifetime risk of ovarian cancer; estimates range from 17% to 44%
Many doctors think that a woman who tests negative for an abnormal BRCA1 or BRCA2 gene but has a first-degree relative (mother, daughter, sister) who tests positive has about the same very high breast cancer risk as someone with an abnormal BRCA1 or BRCA2 gene.
A study has found that isn't true. A woman who tests negative for an abnormal BRCA1 or BRCA2 gene but has a family history of breast cancer and a first-degree relative who's tested positive for BRCA1 or BRCA2 has the same risk of breast cancer as a woman with a family history of breast cancer but no relatives with an abnormal gene.
The results were published online Oct. 31, 2011 in the Journal of Clinical Oncology.
Researchers looked at the medical histories of more than 3,000 families that had one or more women diagnosed with breast cancer. The families were part of the Breast Cancer Family Registry, a project tracking the long-term health of family members. All women who had been diagnosed with breast cancer were tested for abnormal BRCA1 and BRCA2 genes. If the results were positive, all female first-degree relatives also were tested.
Looking at the female first-degree relatives who weren't diagnosed but had genetic testing, the researchers compared the breast cancer risk of the women who tested positive to the risk of the women who tested negative.
Women who didn't have an abnormal BRCA1 or BRCA2 gene were 61% less likely to be diagnosed with breast cancer than women who had an abnormal gene. The women with no abnormal breast cancer genes did have a higher risk of breast cancer than women in the general population. This isn't surprising since they had a family history of breast cancer. Still, their breast cancer risk was much lower than the risk of women with an abnormal breast cancer gene.
Experts have been concerned about the number of women who believe their risk of breast cancer is very high and take aggressive steps to reduce that risk. For example, prophylactic bilateral mastectomy -- removing both healthy breasts to minimize future breast cancer risk -- has been increasing.
Prophylactic mastectomy may make sense for some women with a very high risk of breast cancer who want to aggressively minimize that risk -- a woman with an abnormal breast cancer gene, for example. Still, prophylactic mastectomy shouldn't be done because a woman or her doctor believe her risk is much higher than it really is.
The researchers did this study because they were concerned that doctors may be mistakenly recommending very aggressive risk reduction steps to women who don't have an abnormal breast cancer gene but do have a family history of breast cancer and first-degree relatives with an abnormal gene. The study showed that these women do have higher-than-average risk, but this risk isn't nearly as high as it is for women with an abnormal breast cancer gene. So the steps they take to minimize risk shouldn't be as aggressive as the steps taken by a woman with an abnormal gene.
If you have first-degree relatives with an abnormal breast cancer gene and you haven't been tested, you may want to ask your doctor if genetic testing makes sense for you. If you have an abnormal gene, you should talk to your doctor about all the options you have for reducing your high risk of breast cancer. If you don't have an abnormal gene, your risk of breast cancer is likely much lower than if you did (even if you have relatives with an abnormal gene). You should still take steps to minimize your risk, but very aggressive steps such as bilateral prophylactic mastectomy may not make sense for you.
No matter your BRCA1/BRCA2 status, it's a good idea to work with your doctor to develop a breast cancer screening plan that makes the most sense for your particular situation.
Editor’s Note: This article was updated on Jan. 24, 2019, with updated information on cancer risk associated with BRCA mutations.