Inclusion Criteria:

- 3.1.1 Women who have undergone a core needle biopsy demonstrating an operable breast
cancer whom have not yet had any further therapy.

- 3.1.2 No prior therapy for breast cancer.

- 3.1.4 Age 18 years or older.

- 3.1.5 Any menopausal status

- 3.1.6 Planned surgical resection of breast cancer or repeat core biopsy tissue
sampling prior to initiation of neoadjuvant systemic chemotherapy.

- 3.1.7 Availability of tissue blocks from initial core needle biopsy.

- 3.1.8 Signed informed consent.

- 3.1.9 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:

- 3.2.1 Presence of any Metastatic lesion.

- 3.2.2 History of parathyroid disease, hypercalcemia, or kidney stones.

- 3.2.3 History of SERM or aromatase inhibitor therapy.

- 3.2.4 Taking metformin.

- 3.2.5 History of renal failure requiring dialysis or kidney transplantation.

- 3.2.6 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.)

- 3.2.7 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

- 3.2.8 Patients with locally advanced breast cancer.

- 3.2.9 Any condition potentially interfering with subjects ability to comply with
taking study medication.

- 3.2.10 Any medical condition that would potentially interfere with vitamin D
absorption.

- 3.2.11 Current participation in another research study that would increase risk to
subject, in the opinion of the investigators.

- 3.2.12 Patients currently taking more than 2000 IU of Vitamin D.