Clinical Research Directory

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.