Abstract Background: In women with early-stage breast cancer, the skeleton represents one of the most common sites for metastases and represents approximately 40% of all first recurrences. Preclinical studies demonstrated that inhibition of RANKL significantly delays skeletal tumor formation, reduces skeletal tumor burden, and prolongs survival of tumor-bearing mice. Denosumab, a human IgG2 monoclonal antibody, binds RANKL with high specificity and affinity thus inhibiting RANKL activity. Denosumab has been approved for the prevention of skeletal-related events (SREs) in patients with established bone metastases from solid tumors. Purpose: The D-CARE trial is designed to assess if denosumab treatment prolongs bone metastasis-free survival (BMFS; primary endpoint) in the adjuvant breast cancer setting. Secondary endpoints include disease-free survival (DFS) and overall survival. Additional endpoints include safety, patient reported outcomes (pain, health utilities), as well as exploratory including breast density, time to first on-study SRE following the development of bone metastasis and biomarkers. Methods: In this global, randomized, double-blind, and placebo-controlled phase 3 trial, approximately 4500 women with stage II or III breast cancer at high risk for recurrence were randomized. High risk is defined as biopsy evidence of breast cancer in regional lymph nodes, tumor size > 5 cm (T3), or locally advanced disease (T4). Patients must be receiving or planned to receive standard-of-care adjuvant/neoadjuvant therapy (chemo-, endocrine, or HER-2 targeted), alone or in combination. Patients with a prior history of breast cancer (except DCIS or LCIS) or distant metastasis, oral bisphosphonate (BP) use within 1 year of randomization, or any intravenous BP use, were not eligible. Patients were randomized 1:1 to receive denosumab 120 mg or placebo subcutaneously monthly for 6 months, then every 3 months for a total of 5 years of treatment. Supplemental vitamin D (≥ 400 IU) and calcium (≥ 500 mg) are required. The primary efficacy and two interim efficacy analyses are planned and will be event-driven. The trial, sponsored by Amgen Inc. and registered with the ClinicalTrials.gov identifier NCT01077154, began enrolling patients in June 2010 and completed enrollment in late 2012. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr OT2-6-02.