This study at the University of Wisconsin Carbone Cancer Center in Madison and the Fred Hutchinson Research Center in Seattle, Washington, is investigating whether cadmium, a heavy metal found in the environment, is related to breast density. The researchers will measure the amount of cadmium and other heavy metals found in participants' urine samples. They will also review the participants' recent mammography reports to collect data on breast density. The researchers wanted to enroll up to 1,000 volunteers. The Call to Action for this study was sent to Army of Women members on December 5, 2012. The researchers were able to close enrollment less than 26 hours later, on December 6, 2012, after the Army of Women provided them with 2,580 women who were interested in enrolling in the study.