Epidemiology of breast cancer. Preventive aspects

Descriptive data demonstrate a marked variation in the incidence of breast cancer in distinct populations, which is closely linked to socioeconomic status and correlated with a differential age-specific incidence pattern and time trends. These suggest a westernization effect, and the possible existence of two distinct disease entities--pre- and postmenopausal. Known risk factors may be defined in a number of ways. From a preventive standpoint, a practical classification is suggested whereby risk factors are grouped as preventable, modifiable, unapproachable or spurious. The only risk factors which seem definite at present are estrogen exposure, family history and radiation, with the possible contribution of benign breast disease, replacement hormones, and diet. The only preventable factors are radiation and possibly long-term hormonal replacement, but their contribution to the disease indicence in the population is minimal. Two theoretically modifiable factors are diet and age at first birth, but the latter cannot be easily influenced, and the effect of dietary modification is still unsubstantiated.