The HEAL Study is a prospective cohort study of breast cancer patients recruited through three SEER registries (Fred Hutchinson Cancer Research Center (FHCRC), Seattle, WA, University of New Mexico, and University of Southern California) to assess the associations of weight, physical activity, diet, endogenous hormones, and prognostic factors for breast cancer. The study has enrolled 1183 Stage 0-3a breast cancer cases and has completed 10 year follow-up activities. Follow-up is both active (24- , 60-months, and 10-years to determine recurrences and update exposure variables) and passive (yearly through the respective SEER registries for vital status and second primaries).