This study will assess whether levels of vitamin D impact the characteristics of a woman's breast cancer at diagnosis, and whether a short course of vitamin D in women with low levels of vitamin D changes the gene expression of their breast cancers.

Patients undergoing core needle biopsy of breast abnormalities suspicious for breast cancer will be identified and enrolled in study. As well as those who have had a core needle biopsy demonstrating breast cancer, but who have not yet undergone local surgical treatment, chemotherapy, or hormonal therapy are also eligible. patients with breast cancer on core biopsy will be eligible.

Participants will be assigned to treatment (0, 2000, 4000, 6000 IU/day vitamin D by mouth) based solely on their serum vitamin D levels (Normal: >40 ng/mL; Low-normal: 31-40 ng/mL; Low: 20-30 ng/mL; Very-low: <20 ng/mL). Prior to definitive breast cancer surgery, vitamin D level, parathyroid level, and calcium will be reassessed. Samples of the patients original core biopsy and pathology specimen from their definitive surgical therapy will undergo gene expression profiling.

The ultimate plan is to correlate baseline vitamin D levels with classic prognostic and predictive markers to see if breast cancer biology is impacted by baseline vitamin D level and by vitamin D supplementation and to see if vitamin D supplementation results in gene expression changes similar to those of the vitamin D sufficient group.

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

3 Years