Environmental risk factors and female breast cancer.

The increasing incidence of breast cancer in the United States and the international variation in risk have led to speculation that environmental risk factors are an important cause of breast cancer. We review the epidemiologic evidence on the breast cancer risk associated with ambient environmental exposures experienced passively by the US population, and discuss the difficulties associated with measurement of specific exposures in environmental studies. We review geographic variation of breast cancer rates in the United States, and exposure to organochlorines, ionizing and electromagnetic radiation, and passive smoking. Results are inconclusive but do not support a major role of environmental risk factors in the etiology of breast cancer.