Breast Cancer Risk in Women with Mutations in BRCA1 or BRCA2

True disease risk associated mutations in the BRCA1 and BRCA2 genes (often referred to as “deleterious” in genetic testing reports) result in a markedly elevated lifetime risk of breast cancer in women.

Risk estimates vary tremendously.  This often depends on how the study that they came from was designed.  We’ll try to break this complicated topic down into understandable terms in a future whitepaper, but for the time being, here is some basic information about breast cancer risk associated with having a mutation in either the BRCA1 or BRCA2 gene.

Background Risks of Breast Cancer in the General Population

The risk of being diagnosed with breast cancer by age 80 for a woman northern European descent in the United States is about 12% (or a 1 in 8 chance).  This also means that there is about an 88% chance that she will not develop breast cancer by age 80.

Risks vary somewhat with ethnic and racial background, in addition to other risk factors.  In the future, we will add a more extensive discussion of this topic; however, since this website is primarily focused on information for women known already to be at high risk, we would recommend the U.S. National Cancer Institute Breast Cancer Risk Assessment Tool site as an excellent resource for general information on breast cancer risk.

Breast Cancer Risk in Women with a BRCA1 Mutation

Women with mutations in BRCA1 are thought to have lifetime risks for breast cancer diagnosis of approximately 50 to 85 percent.  This means that the chance that they will not be diagnosed with breast cancer during their lifetime is about 15 to 50 percent.

It is important to remember that these risk levels can be modified with risk reducing procedures.  Women who proactively pursue strategies to decrease their risk can anticipate that these strategies will lower their risks.

Breast Cancer Risk in Women with a BRCA2 Mutation

Lifetime breast cancer risks in women with a BRCA2 mutation are similar to those in women with a BRCA1 mutation.  Some of the same challenges to accurately estimating these risks apply.

As for women with BRCA1 mutations, risk reducing surgical procedures have the potential to significantly decrease breast cancer risk in women with BRCA2 mutations.

Some Key References

Antoniou A, Pharoah PD, Narod S, et al. Average risks of breast and ovarian cancer associated with BRCA1 or BRCA2 mutations detected in case series unselected for family history: a combined analysis of 22 studies.  American Journal of Human Genetics 2003; 72:1117-30.

Chen S, Iversen ES, Friebel T, et al. Characterization of BRCA1 and BRCA2 mutations in a large United States sample.  Journal of Clinical Oncology 2006; 24:863-71.

Chen S, Parmigiani G.  Meta-analysis of BRCA1 and BRCA2 penetrance.  Journal of Clinical Oncology 2007; 25:1329-33.

Evans DG, Shenton A, Woodward E, et al. Penetrance estimates for BRCA1 and BRCA2 based on genetic testing in a Clinical Cancer Genetics service setting: risks of breast/ovarian cancer quoted should reflect the cancer burden in the family.  BMC Cancer 2008; 8:155.

Risch HA, McLaughlin JR, Cole DE, et al. Population BRCA1 and BRCA2 mutation frequencies and cancer penetrances: a kin-cohort study in Ontario, Canada.  Journal of the National Cancer Institute 2006; 98:1694-706.