Having an abnormal BRCA1 (BReast CAncer gene one) or BRCA2 (BReast CAncer gene two) gene can increase breast cancer risk. A study reports that the amount of this increased risk can vary widely. The increased risk also varies widely among relatives of people with an abnormal BRCA1 or BRCA2 gene.
The higher risk of breast cancer in people with an abnormal BRCA1 or BRCA2 gene has been the focus of many studies. But this one of the first times doctors have looked at how this higher risk varies among people with an abnormal breast cancer gene and their relatives.
The difference in risk depends on when and where breast cancer is diagnosed in the person with the abnormal gene.
Breast cancer risk may be much higher if the person with the abnormal gene had breast cancer diagnosed at a young age or in both breasts. Breast cancer risk may be not as increased if the person with the abnormal gene had breast cancer diagnosed later in life. These differences in risk are likely because there are different types of BRCA1 and BRCA2 abnormalities. These different gene abnormalities affect breast cancer risk differently.
Most women who develop breast cancer do NOT have an inherited abnormal breast cancer gene. Abnormal BRCA1 and BRCA2 genes account for about 10% of all breast cancers. Women with an abnormal BRCA1 or BRCA2 gene have up to an 85% risk of developing breast cancer by age 70. Based on the study reviewed here, this risk may be lower than 85% for many women with an abnormal gene or who have a relative with an abnormal gene. Of course, this depends on the type of gene abnormality and the details of the breast cancer diagnosis. In the future, doctors may be able to identify the specific BRCA1 or BRCA2 abnormality and the increase in risk associated with that abnormality.
To learn more about genes and breast cancer, visit the Breast Cancer Risk Factors: Genetics page.