Vitamin D and Breast Cancer Biomarkers in Female Patients

OBJECTIVES: Primary * To evaluate change in mammographic density using the Boyd method after one year of vitamin D supplementation compared to placebo in premenopausal women. Secondary * To explore changes in the serum biomarker IGF1 in response to one year of vitamin D or placebo supplementation in premenopausal women. * To explore changes in cellular proliferation (atypia and Ki67) in response to one year of vitamin D or placebo supplementation in premenopausal women. * To explore correlations between change in breast cancer biomarkers (density, IGF1, atypia, and Ki67) with each other and with change in vitamin D levels. * To compare methods of mammographic density analysis. * To validate a recently developed sunlight questionnaire. OUTLINE: This is a multicenter study. Patients are stratified according to baseline vitamin D (sufficient \[≥ 30 ng/mL or ≥ 75 mmol/L\] vs insufficient \[\< 30 ng/mL or \< 75 mmol/L\]) and institutional random periareolar fine-needle aspiration (RPFNA) status (performs RPFNA vs does not perform RPFNA). Patients are randomized to 1 of 2 treatment arms. * Arm I: Patients receive oral placebo once daily for 12 months. * Arm II: Patients receive oral vitamin D (2000 IU) once daily for 12 months. Tissue and blood samples are collected at baseline and at 12 months for laboratory biomarker analysis. Patients also complete questionnaires at baseline and at 12 months.