|Increasing age. Besides being female, age is the single most important risk factor for breast cancer. More than 75 percent of all breast cancers occur in women over 50.
Family history of breast cancer. History of breast cancer in a first-degree relative (mother, sister or daughter) is associated with the largest increase, especially when the relative is diagnosed at an early age.
History of benign breast disease. Several studies have suggested that the increased risks associated with benign breast disease may be confined primarily to women with diagnoses of atypical hyperplasia.
Hormonal factors. Early age at menarche, late age at menopause, late age at first live birth, and few pregnancies all increase a womans risk of breast cancer, possibly all of them by affecting her lifetime exposure to hormones. Scientists postulate that hormones may promote cell division in breast tissue and increase the risk of mutations
Breast cancer genes. Hereditary breast cancer occurs at younger ages, is more likely to be in both breasts and often appears in multiple family members over three or more generations, including women from the paternal side of the family. Approximately 5-10 percent of breast cancers are believed to be inherited. In 1994, researchers isolated two breast cancer susceptibility genes ? BRCA1 and BRCA2 ? which together are estimated to account for 40-50 percent of all hereditary breast cancers.
Oral contraceptives and estrogen replacement therapy. Recent use of oral contraceptives may slightly increase the risk of breast cancer; however, women who stopped using oral contraceptives at least 10 years in the past have the same risk as women who have never used the Pill. Long-term estrogen replacement therapy also appears to increase risk.
In addition, Caucasians, women of high socioeconomic status and those with exposure to high doses of ionizing radiation are at risk for breast cancer.