[Female sex hormones increase the risk of breast cancer].

The incidence of breast cancer in women in increasing, partly due to changes in age distribution in the population, and partly due to a real increase in risk. Changes in family patterns may, to some extent, explain the increased risk since giving birth to a first child late in life and bearing few children both increase the risk of breast cancer. The influence of female sex steroids on the breast plays a central role, but the biological mechanism is not clearly understood. There is a certain amount of risk involved in using hormonal medication (oral contraceptives or postmenopausal hormone replacement), but on ceasing to take the medication, risk will revert to the expected rate within a few years. Future epidemiological research on breast cancer will concentrate on events occurring during hormonally potent phases of life, such as growth and development during the fetal period, and sexual and somatic maturation during adolescence. Until now only modest interest has been shown in researching these two particular phases, but both may be important for the natural course of breast cancer.