Inclusion Criteria:

• Women with a diagnosis of hormone receptor positive invasive breast cancer (Stage I-IIIB) •Postmenopausal status •Completed at least 8 weeks of anastrozole as adjuvant therapy prior to study entry •Completed systemic chemotherapy and radiation treatments when indicated •Serum Calcium < 10.3 mg/dL •Marginal 25 OH Vitamin D level (between 10 and 29 ng/ml) •24-hour urine Calcium excretion < 250 mg/g •A history of generalized musculoskeletal pain with or without localized regions of discomfort that has developed or worsened since starting adjuvant aromatase inhibitor therapy

Exclusion Criteria:

•Known metastatic disease •History of kidney stones •History of active primary hyperparathyroidism •History of Paget’s disease of the bone •History of severe arthritis, rheumatoid arthritis, or severe neuropathy •History of medical or psychiatric condition which may preclude protocol compliance •Normal 25 OH vitamin D level (>30 ng/ml)