Genetic testing can determine if a woman has inherited mutations to the so-called "breast-cancer genes" known as BRCA1 and BRCA2, which predispose her to breast and ovarian cancer, but only accounts for 5 to 10 percent of all breast cancers. Genetic counseling and testing may be considered for women with two or more first-degree relatives (mother, sister, daughter) with breast and/or ovarian cancer. Although a positive result on a genetic test indicates increased risk of developing breast cancer, it cannot predict with certainty that you will ever get the disease.

Similarly, a negative result is not a guarantee that you will not get breast cancer; it just means that if you do develop the disease, it is unlikely to be the inherited familial type.

Other factors that can increase the risk of breast cancer include never having had children and having had a late menopause. Diet also may be a risk factor for breast cancer. Studies have shown a higher prevalence of breast cancer among cultures with high-fat diets compared with those that consume lower amounts of dietary fat. However, it is unknown if switching to a low-fat diet actually decreases the risk of breast cancer. Hormones produced by the ovaries, such as estrogen, also appear to increase a woman's risk for developing breast cancer.