Cells in the breast that grow out of control can be normal (benign, not cancerous) or abnormal (malignant, cancerous.) Breast cancer can grow and invade tissue surrounding the breast to form new tumors. The exact cause of breast cancer is unknown, but certain risk factors such as a woman's age, family history, personal history and diet can contribute to one’s risk.
Breast cancer can occur in men, but it is more common in women. Increasing age is the most common risk factor for developing breast cancer. Only 5% to 10% of breast cancers are inherited from gene mutations. Blood tests may identify genes that cause breast cancer. These tests may be recommended if you have a strong family history of the disease. However, having one or more breast cancer risk factors doesn't mean that you will actually develop breast cancer. Some women have no risk factors but still develop breast cancer.
Other risk factors include first pregnancy at an older age or never having been pregnant, older age at the beginning of menopause, younger age (12 years or under) at menstruation, obesity, previous radiation exposure and drinking alcohol.