Fixed and modifiable risk factors for breast cancer.

Likely pathogenesis of breast cancer is in two phases, initiation and promotion. Initiating factors include ionising irradiation, dietary factors and possibly alcohol consumption causing DNA mutations uncorrected by repair mechanisms. Subsequent promotional factors include exposure to oestrogens, reduced by late menarche, early pregnancy and lactation and increased by nulliparity, oral contraceptive use and hormone replacement therapy. Only 5% of breast cancers result from inherited genetic mutations of BRCA1 and BRCA2, but individuals with such mutations have a high risk (66-80%) of developing the disease. Most patients with benign breast problems are not at increased risk of breast cancer, but those with atypical epithelial hyperplasia have an increased risk and should be kept under surveillance or asked to participate in trials of prevention.