About 5% to 10% of breast cancer cases are thought to be hereditary, meaning that they result directly from gene changes (mutations) passed on from a parent. BRCA1 and BRCA2 : The most common cause of hereditary breast cancer is an inherited mutation in the BRCA1 or BRCA2 gene . In normal cells, these genes help make proteins that repair damaged DNA . Mutated versions of these genes can lead to abnormal cell growth, which can lead to cancer . If you have inherited a mutated copy of either gene from a parent, you have a higher risk of breast cancer. On average, a woman with a BRCA1 or BRCA2 gene mutation has up to a 7 in 10 chance of getting breast cancer by age 80. This risk is also affected by how many other family members have had breast cancer. (It goes up if more family members are affected.) Women with one of these mutations are more likely to be diagnosed with breast cancer at a younger age, as well as to have cancer in both breasts. Women with one of these gene