Objective: To evaluate the efficacy and safety of QL1206 (a denosumab biosimilar to Xgeva (R)) in breast cancer patients with bone metastasis (BM) through subgroup analysis of a randomized, double-blind phase III trial (No. NCT04550949). Methods: This subgroup analysis included patients with BM from breast cancer enrolled in a phase III trial. Patients were randomized (1:1) to receive either three cycles of QL1206 or denosumab (120 mg subcutaneously every 4 weeks). Subsequently, they received 10 cycles of QL1206 (120 mg) over 40 weeks, followed by a 20-week safety follow-up. The primary endpoint was the percentage changes from baseline to week 13 in urinary Ntelopeptide corrected for creatinine (uNTx/Cr). Results: The breast cancer cohort consisted of 311 patients. Vertebral involvement (66.4%) was the most prevalent BM site at enrollment, while 27.7% of patients presented with >= 3 metastatic bone lesions. At week 13, QL1206 demonstrated a median uNTx/Cr reduction of-69.9% (range: -98.1%-568.0%) vs. -74.3% (range: -97.7%-386.3%) for denosumab. The analysis of covariance revealed comparable least-square means for log transformed changes: -1.416 [95% confidence interval (95% CI): -1.736 to-1.096] vs. -1.501 (95% CI: -1.824 to-1.178), yielding an between-group difference of 0.085 (90% CI: -0.062-0.232; P=0.343). After a 53-week treatment period, 83.6% achieved bone density improvement/disease stabilization. Safety profiles were comparable between groups. Conclusions: QL1206 demonstrated similar efficacy and safety to the reference denosumab in patients with BM from breast cancer, supporting QL1206 as a new option for management of BM from breast cancer.