Epidemiology, prevention, and early detection of breast cancer.

Breast cancer is the most common cancer among women worldwide. Genetic, environmental, and gene-environment interactions are discussed in relation to breast cancer etiology. A major advance in the study of inherited forms of breast cancer occurred with the identification of two genes, BRCA1 and BRCA2, that may account for a majority of inherited forms of breast cancer cases. Hypotheses have been formulated concerning the importance of timing of exposures to environmental agents and a possible role of "xenogenetics" in relation to breast cancer risk. With respect to early detection, regular mammography screening for women aged 50 years and older is clearly associated with a significant reduction in breast cancer mortality, but mammography among women aged 40 to 49 remains controversial. Concerning chemoprevention, the risks and benefits of tamoxifen continue to be clarified, retinoids hold promise, and monoterpenes have emerged as a possible chemopreventive agent.