Sherry Boyer, a genetic counselor at Memorial Sloan-Kettering Cancer Center, explains why some women have a higher risk of developing breast cancer. Most women over age 50 have about a 12.5 percent chance of developing the disease. Having a family member with the disease increases a woman’s risk to about 20 percent. Inheriting mutations in the genes BRCA1 and BRCA2 increase the risk to more than 50 percent. While hereditary breast cancer is relatively rare, it is much more common in certain ethnic groups such as Ashkenazi Jews.