Real-world data of efficacy and safety of denosumab on patients with breast cancer with bone metastasis: Results from Chinese clinical experience.

e13103 Background: Bone is the most common metastasis site in advanced metastatic breast cancer disease. Denosumab is advocated by various guidelines with high-quality of evidence for the treatment of breast cancer patients with bone metastases (BM) to delay or reduce the occurrence of skeletal related events (SRE). Data for bone lesion repair after treatment on image is still needed in real world. This retrospective study aims to evaluate the efficacy of denosumab on breast cancer with BM by MD Anderson (MDA) criteria which is specific to BM and its safety in real world. Methods: Data of patients age ≥18 years diagnosed with advanced breast cancer with BM and treated with denosumab from June 1 st 2020 to Dec 31 st 2022 were retrospectively analyzed. The primary endpoint was the objective response rate (ORR) for bone lesions by MDA criteria in evaluable patients. Secondary endpoints include disease control rate (DCR) for bone lesions, risk of SRE occurrence and safety in total population. Subgroup analysis investigated the impact of the time of denosumab treatment initiation post-diagnosis of BM as well as the duration of treatment with denosumab on efficacy. Comparative analysis was performed using Chi-squared test and a p value of 3 months were 31.54% vs. 6.15% (p<0.001) and 68.46% vs. 21.54% (p<0.001), respectively. The ORR and DCR for bone lesions of the duration of denosumab treatment <6 months vs. ≥6 months were 4.62% vs. 33.08% (p<0.001) and 37.69% vs. 76.92% (p<0.001), respectively. Renal function impairment decreased from 33 patients before treatment to 8 patients post-treatment, while hypocalcemia increased from 1.62% to 11.35%. Osteonecrosis of the jaw occurred in one patient (1/185,0.54%) post-treatment. Conclusions: Denosumab was found to be effective and safe for breast cancer patients with BM in this large retrospective study. Early initiation and longer duration of denosumab treatment may generate better clinical outcomes for bone lesions by MDA criteria.