It is the goal of this proposal to look at genes, environment, clinical co-factors, and, if possible, any interactions in breast cancer. The ultimate objective of these studies is to establish an effective way of identifying individuals at greatest risk for cancer. We will evaluate the risk of breast cancer associated with polymorphisms in genes involved in estrogen metabolism and action. We will also evaluate the association of breast density and polymorphisms in genes associated with estrogen metabolism and action. In addition, we will also evaluate nipple aspirate fluid and breast duct lavage fluid as another potential source of promising biomarkers of risk.