Tamoxifen-MRI Study

The project is a double blind, randomized, placebo-controlled phase II chemoprevention trial. The study outcomes will be biological markers, rather than cancer incidence or mortality. Eligible study subjects will be women, between the ages 25-45, whose calculated lifetime breast cancer risk is \> 20% (25% by the Couch model). Study participants will be randomly assigned to receive either tamoxifen or placebo for one year. Participants will subsequently be followed for one year off of medication. The primary objective is to evaluate the effectiveness of tamoxifen in reducing breast density by mammogram. Mammographic density has been correlated with breast cancer risk and reduced breast density may have the added benefit of improving the sensitivity of breast cancer screening in young women. Breast density will be employed as a marker of progression-related - proliferative - mechanisms of carcinogenesis. Secondary study outcomes will include estrogen ratios (catechol estrogen/estradiol), 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.