A Study of Romosozumab in People With Breast Cancer and Osteoporosis

Inclusion Criteria: * ≥18 years of age at the time of giving informed consent; * Patients diagnosed with hormone-receptor positive (ER/PR \>1%) metastatic breast cancer to bones on any endocrine therapy with or without targeted therapy (i.e. CDK 4/6 inhibitors, PI3K inhibitors, anti-HER2-therapy); * Evidence of osteoporosis on dual X-ray absorptiometry (DXA) scan; must following: * osteoporosis on dual X-ray absorptiometry (DXA) scan; or history of fragility fracture of the spine or hip; or of morphometric spine fracture; Exclusion Criteria: * Prior therapy with a bone-modifying agent (intraveous bisphosphonates or subcutaneous denosumab) for metastatic bone disease; * 25 (OH) vitamin D levels \< 20 ng/mL; Vitamin D repletion will be permitted and subjects will be be rescreened once 25 (OH) vitamin D level ³ 20 ng/mL; * History of myocardial infarction or stroke within the preceding year; * Current hyper- or hypocalcemia, defined as albumin-adjusted serum calcium outside the normal range per institutional standard (\<8.5 or \>10.5 mg/dL); Calcium repletion will be permitted and subjects will be be rescreened once values are within the institutional standard. * History of non-healed dental or oral surgery; * History of osteonecrosis of the jaw