PRIMARY OBJECTIVES: I. To assess whether magnetic resonance imaging (MRI) volume (equivalent to 3-dimensional mammographic density) is reduced in high-risk women or those with invasive breast cancer or DCIS who are supplemented daily with soy (5p mg total isoflavones as aglycone) compared to placebo (microcrystalline cellulose) tablets for 1 year.II. To assess whether cell proliferation and apoptosis, as measured by Ki67 and caspase 3 staining, respectively, of breast epithelial cells is altered with soy treatment.SECONDARY OBJECTIVES: I. To assess whether other intermediate molecular markers including estrogen receptor alpha (ER alpha) and ER beta differ between women supplemented with soy vs placebo. OUTLINE: Patients are randomized to 1 of 2 treatment arms.ARM I: Patients receive oral soy isoflavones supplement once daily for12 months in the absence of disease progression.ARM II: Patients receive oral placebo once daily for 12 months in the absence of disease progression.