There is no doubt that breast cancer can run in families, so it's likely that there is a hereditary factor. It is important to note that only about 10 percent of women diagnosed with breast cancer have a family history. Just because one of your relatives had breast cancer does not mean you are absolutely fated to develop it.
Scientists have identified two genes, BRCA 1 and BRCA 2, that seem to be associated with an increased risk for breast cancer. In fact, five to ten percent of women diagnosed with breast cancer will be carriers of one of these mutations.