Statement: Candidates with hyperparathyroidism are automatically excluded from the primary trial.
Primary_evidence: INCLUSION CRITERIA:   Undergoing core needle biopsy for a breast abnormality suspicious for breast cancer.   Has undergone a core needle biopsy demonstrating breast cancer and has not yet had any further therapy, provided the core needle biopsy is available for analysis.   No prior therapy for breast cancer within the past 5 years.   18 years of age or older.   Ability to understand and the willingness to sign a written informed consent document. EXCLUSION CRITERIA:   History of parathyroid disease, hypercalcemia, or kidney stones.   Supplemental vitamin D other than from a standard multiple vitamin or from standard formulations of calcium and vitamin D (eg, calcium citrate with vitamin D) within the prior 6 months.   History of renal failure requiring dialysis or kidney transplantation.   Pregnant or nursing   Receiving supplemental calcium > 1200 mg calcium per day during study.   Initial treatment of breast cancer will not be with breast-conserving surgery or mastectomy.   Locally-advanced breast cancer   Plans for neoadjuvant chemotherapy, hormonal therapy, or other systemic therapy   Plans for preoperative radiation therapy   Plans for breast cancer surgery, and does not allow for at least 10 days of vitamin D intervention.   Any condition potentially interfering with subjects ability to comply with taking study medication.   Any medical condition that would potentially interfere with vitamin D absorption, such as celiac sprue, ulcerative colitis.   Current participation in another research study that would increase risk to subject, in the opinion of the investigators