At Significantly Higher Risk 
• History of previous cancer in one breast, especially if it occurred before menopause.

At Slightly Higher Risk 
• Increasing age.
• Family history of breast cancer, primarily in parents, daughters and sisters, but also in second-degree relatives
  such as aunts, cousins and grandmothers. This is true for relatives on the father's side as well as the mother's.
  (Genetic markers are becoming available to screen for some forms of familial breast cancer.) The risk is about 6
  times greater if a mother or sister had breast cancer before menopause, and up to 10 times greater if the cancer
  was in both breasts. A specific gene for familial breast cancer has been discovered (17q21). 
• Carriers of the familial breast cancer gene BRCA-1, which is associated with a high risk of developing breast
  cancer and transmitting this risk to offspring.
• Some premalignant breast lesions may be associated with development of breast cancer, including multiple
  papillomatosis, atypical hyperplasia and, occasionally, very large cysts in the breast (not the more common
  and smaller fibrocystic breast condition). Most women with fibrocystic changes are not at increased risk
  because of them. There is no relation between these palpable breast changes and the risk of cancer.
• There is a slightly higher risk for women who have never carried a term pregnancy or who were first pregnant
  after age 30.