 Genetic predisposition

Between 5 percent and 10 percent of breast cancers are inherited. Defects in one of several genes, especially BRCA1 or BRCA2, put you at greater risk of developing breast, ovarian and colon cancers. Usually these genes help prevent cancer by making proteins that keep cells from growing abnormally. But if they have a mutation, the genes aren't as effective at protecting you from cancer.