Effects of once-yearly zoledronic acid on bone density and incident vertebral fractures in nonmetastatic castration-sensitive prostate cancer patients with osteoporosis

BACKGROUND: Androgen deprivation therapy (ADT) is the effective treating prostate cancer but is often accompanied by cancer treatment-induced bone loss (CTIBL), which impairs the patient’s quality of life. In patients with nonmetastatic castration-sensitive prostate cancer (M0CSPC) who already have osteoporosis before starting ADT, appropriate bone-modifying agent intervention must be performed in parallel, as the patient has a high risk of future fracture. However, little is known about therapeutic interventions aimed at preventing the progression of CTIBL and new fractures. The present study explored the effect of once-yearly zoledronic acid 5 mg (ZOL 5 mg) on bone mineral density (BMD) and new vertebral fractures (VFs) in M0CSPC patients with coexisting osteoporosis before starting ADT. METHODS: We conducted a retrospective, multi-institutional, cohort study involving 42 M0CSPC patients with osteoporosis who had undergone ADT with/without a single intravenous infusion of ZOL 5 mg at the start of ADT (ZOL 5 mg group, n = 26; control group, n = 16). The association of the ZOL 5 mg with changes in the BMD from baseline to 12 months and the incidence of VFs were evaluated. RESULTS: Prevalent VFs were found in 47.6% of all patients at baseline. ZOL 5 mg significantly increased the lumbar spine BMD (LS-BMD) (mean rate of change: + 4.02%, p < 0.0001) and significantly decreased the TRACP-5b (mean rate of change: − 52.1%, p < 0.0001) at 12 months after starting ADT. Incident VFs were identified in 19.0% of all patients at 12 months after starting ADT. After adjusting for the age, BMI, and changes in the LS-BMD, ZOL 5 mg was not significantly associated with incident VFs (odds ratio 0.66, 95% confidence interval 0.04–11.3, p = 0.7774). CONCLUSION: ZOL 5 mg significantly increased the LS-BMD 12 months after starting ADT, and our short-term results showed that ZOL 5 mg was not significantly correlated with the suppression of incident vertebral fractures.