In many regards, a discussion of the risk factors for breast cancer is a bit misleading, and can give many women a false sense of security. This is not to say that risk factors are to be disregarded, because women with one or more risk factors should be especially careful to be screened properly. The important thing to remember is that having no risk factors should not give you a false sense of security.
More details are below.
Breast cancer, like many cancers, increases in risk as a woman gets older. A personal history of breast cancer in one breast increases a woman's risk of developing breast cancer in the other breast by a factor of five times. The risk might even be higher than five times greater if the original cancer developed before age 50. Women who have close relatives who have had breast cancer appear more likely to develop the disease than women with no such family history. This risk might even be stronger for women whose relatives developed the disease before menopause.