Oestrogens and breast cancer: exogenous hormones

Oestrogens are administered to women as contraceptive agents and as treatment for menopausal symptoms. This article reviews the epidemiological evidence concerning the risk of breast cancer related to both types of medication. It is generally accepted that long-term; high-dose menopausal oestrogen administration without accompanying progestogen is associated with a moderate increase in breast cancer risk; and that combined oral contraceptives reduce the risk of benign breast disease (as well as ovarian and endometrial cancer). The effect of oral contraceptives on breast cancer risk, however, is less certain. Possible reasons for the lack of agreement between recently conducted case-control studies are discussed, concentrating specifically on the effect of possible latency, being the sum of a prolonged induction plus pre-clinical period, in explaining the discrepancies.