<qa>  What is the primary study outcome?Secondary study outcomes will include estrogen ratios catechol estrogenestradiol, and markers of oxidative DNA damage in peripheral blood and urine markers of progression-related mutational - events in carcinogenesis. The responsiveness of these outcomes will suggest the mechanisms through which tamoxifen exerts its preventive effect. Persistence of the markers after one year of treatment may also provide early information about the anticipated duration of the tamoxifen effect. 