Development of Vitamin D as a Therapy for Breast Cancer - Phase 2

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