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