Risk factors for breast cancer.

Breast cancer is multifaceted, and multiple risk factors most likely contribute to each case of the disease. Through further elucidation of highly penetrant autosomal dominant mutations and, perhaps more importantly, weaker polygenic influences, rational therapies to treat or prevent malignancy may develop. Determining the nature and sequence of genetic changes in premalignant breast tissue may offer the greatest opportunity to alter the process of breast cancer development. Perhaps the most difficult challenge is to understand the environmental risk factors that predispose to breast cancer. Although endogenous factors such as hormonal influence on breast cancer risk have been established, this information has not greatly affected our ability to prevent or significantly reduce the risk of disease. National and regional collaborative efforts are needed to fund research directed at defining how the environment and lifestyle factors affect the risk of cancer development.