Only about 13 percent of women diagnosed have a first-degree female relative (mother, sister or daughter) with breast cancer. Most women with breast cancer do not have a family history of the disease so breast cancer screening is important for women without a family history. If your mother, sister or daughter has been diagnosed with breast or ovarian cancer a more aggressive screening schedule starting before age 45 may be very important.
If you have a first-degree female relative with breast cancer your risk is double that of a woman without a family history. If you have more than one first-degree female relative with a history of breast cancer, your risk is three or four times greater. The younger your relative was when diagnosed, the greater the chance of breast cancer.
By comparison, a woman whose mother was diagnosed with breast cancer before age 40 has about twice the risk of a woman without a family history... For a woman whose mother was diagnosed at an older age, the increase in risk isn’t as high.
Family histories with male breast cancer or prostate cancer first-degree relatives (father or brother) is also an indication of an increased risk of breast cancer, especially if the cancer was found at a young age. (Some studies indicate this may double the chance of breast cancer in daughters or sisters.)