Vitamin D and Breast Cancer: Does Weight Make a Difference?

Inclusion Criteria:

* Women who have undergone a core needle biopsy demonstrating an operable breast cancer whom have not yet had any further therapy.
* No prior therapy for breast cancer.
* Age 18 years or older.
* Any menopausal status
* Planned surgical resection of breast cancer or repeat core biopsy tissue sampling prior to initiation of neoadjuvant systemic chemotherapy.
* Availability of tissue blocks from initial core needle biopsy.
* Signed informed consent.
* Willing to discontinue use of all supplements containing Vitamin D for the duration of the study, and take only the Vitamin D provided by the study.

Exclusion Criteria:

* Presence of any Metastatic lesion.
* History of parathyroid disease, hypercalcemia, or kidney stones.
* History of Selective estrogen receptor modulator (SERM) or aromatase inhibitor therapy.
* Receiving metformin.
* History of renal failure requiring dialysis or kidney transplantation.
* Women who are known to be pregnant or who are nursing. (As vitamin D does not have toxicity to the fetus, a negative pregnancy test is not a requirement to participate in the study.)
* Patients planned for surgical therapy of their breast cancer or initiation of systemic chemotherapy, that would not allow for at least 7 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.
* Current participation in another research study that would increase risk to subject, in the opinion of the investigators.
* Patients currently taking more than 2000 IU of Vitamin D.