RETHINKING BREAST-CANCER RISK AND THE ENVIRONMENT - THE CASE FOR THE PRECAUTIONARY PRINCIPLE

The World Health Organization recently reported that breast cancer has become the most common cancer in women throughout the world. Known ri sk factors account for less than half of all cases of breast cancer, a nd inherited germ line mutations occur in at most only 10% of all case s. Cumulative exposure to estradiol and other hormones links many of t he established risk factors for breast cancer. This paper reviews epid emiologic and toxicologic evidence on breast cancer risks and presents a comprehensive construct of risk factors intended to focus on the id entification of those factors that can be controlled or modified. We a ttempt to provide a framework for interpreting the etiologic interplay of endogenous metabolic changes and environmental changes in the etio logy of breast cancer. The construct we develop distinguishes between those risk factors that are directly causal, such as ionizing radiatio n and inherited germ cell defects, those vulnerability factors that ex tend the time period during which the breast undergoes development, an d those contributing factors that increase total hormonal stimulation of the breast. Some hormonally active compounds, such as those in soy and broccoli and other phytoestrogen-containing foods, can be protecti ve against breast cancer, while others, such as some environmental con taminants, appear to increase the risk of the disease by increasing le vels of harmful hormones. Efforts to explain patterns of breast cancer should distinguish between these different risk factors. Identificati on of vulnerability and contributing risk factors can foster the devel opment of public policy to reduce the burden of this prevalent cancer, prudent precautionary principles suggest that reducing exposure to av oidable or modifiable risk factors should receive high priority from t he public and private sectors.