Frequently Asked Questions

How do alterations in the BRCA1 and BRCA2 genes affect a woman's risk for breast and ovarian cancers?

A woman's lifetime risk for breast and ovarian cancers greatly increases if she has an altered BRCA1 or BRCA2 gene. Women who have inherited these gene alterations usually have an increased risk of developing breast cancer at a younger age (before menopause), and they often have multiple close family members with the disease. Because most research has been done with large families with many affected individuals (people with cancer), estimates for the risk of developing breast and/or ovarian cancers in women with these gene alterations may be artificially high. Recent studies with women more representative of the general population have found somewhat lower estimates. Therefore, numbers for breast and/or ovarian cancer risk in persons with altered BRCA1 and BRCA2 genes should be viewed as broad ranges that may change as more research data are added.

According to lifetime risk estimates for women in the general population, about 12% (120 out of 1000 individuals) will develop breast cancer, compared with 50 to 85% (500-850 out of 1000) of women with an altered BRCA1 or BRCA2 gene. For ovarian cancer, lifetime risk estimates for women in the general population predict that 1.5% (15 out of 1000) will get ovarian cancer, compared with 5 to 40% (50-400 out of 1000) for women with an altered BRCA1 gene, and 10 to 20% (100-200 out of 1000) for women with an altered BRCA2 gene.

These wide ranges of risk estimates reflect the fact that actual risks will be different from one woman to another. Although these estimates can be useful for considering risk in large groups of people, they cannot predict an exact risk for cancer in any one individual.

NCI, Genetic Testing for Breast Cancer Risk: It's Your Choice, 1997.