The involvement of oestrogen in the development and progression of breast disease: epidemiological evidence

SynopsisThe epidemiological approach to the investigation of breast cancer is briefly described with special reference to case-control and cohort studies. Risk factors for breast cancer are then reviewed, paying particular attention to menstrual and reproductive factors and to body weight. Some of the hypotheses which attempt to draw the epidemiological observations together are also outlined.The effects of exposure to exogenous oestrogens are considered in more detail. There is evidence from one study that the administration of large doses of stilboestrol during pregnancy increases breast cancer risk after a latent interval of about twenty years. Conjugated equine oestrogens administered to postmenopausal women may also slightly increase breast cancer risk after prolonged use. Little information is available about the effects of any other type of “hormone replacement therapy”. Combined oral contraceptives do not appear to have any general effect on breast cancer risk, but prolonged early use, especially use before first term pregnancy, may be harmful to the breast.