Zoledronic acid and skeletal-related events in patients with bone metastatic cancer or multiple myeloma

Introduction: Investigations of ZA effectiveness using large, real-world databases are rare. We examined whether zoledronic acid (ZA) decreased the risk of skeletal-related events (SREs) among patients with bone metastases (BMs) from breast cancer (BC) or prostate cancer (PC), or multiple myeloma (MM) in routine clinical practice. Materials and methods: We conducted a propensity score-matched cohort study using the Korean National Health Insurance database. Our cohort included patients diagnosed with BM after BC or PC, or MM between 2004 and 2015. SRE was defined as having a record of pathologic fracture, spinal cord compression, radiation, or surgery to bone. The incidence of multiple SREs was calculated according to SRE history. We calculated the incidence rate ratio (IRR) to examine the relative difference in the risk of SREs of ZA users compared to those of ZA non-user. Results: Among 111,679 patients, diagnosed with BM and one of the three cancer types, 5608 were included in the analysis after propensity score matching. A decreased risk of SREs was observed for the ZA use in patients with history of SRE in BC [IRR = 0.74, 95% confidence interval (CI) = 0.66–0.83], PC (IRR = 0.86, 95% CI = 0.73–1.02), and MM (IRR = 0.74, 95% CI = 0.59–0.93). For patients without SRE history, ZA use was not associated with decreased risks of SREs, but rather increased the risks (BC: IRR = 1.96, 95% CI 1.87–2.05; PC: IRR = 1.66, 95% CI 1.54–1.80; MM: IRR = 1.92, 95% CI 1.57–2.34). Conclusions: Our study suggests that the ZA use was associated with a decreased risk of SRE for patients with SRE history. However, no preventive effects of ZA were observed for patients without history.