BRCA1 and breast cancer: Risk factors for developing breast cancer include increasing age, female gender, previous history of breast cancer, histologic abnormalities on breast biopsy, family history of breast cancer, genetic mutations such as BRCA1 and BRCA2, younger age at onset of menarche, nulliparity, menopause after the age of 55, exogenous hormone use such as hormone replacement therapy, and other external factors such as radiation and environmental exposure, excessive alcohol consumption, and obesity.