Purpose: To evaluate the effects of timing and length of zoledronic acid (ZA) treatment on outcomes for patients with prostate cancer in clinical practice. Materials and methods: Patients with prostate cancer and first bone metastasis diagnosed from January 2003 to October 2006 were included. Patients were considered 'untreated' if no ZA was given, 'early ZA-treated' if ZA was initiated before skeletal complication (SC) occurrence or 'late ZA-treated' if one or more SC was documented before or at ZA initiation. Patients were classified with short (90 days), medium (91180 days) or long (>180 days) treatment persistence. Assessments included follow-up duration (FUP) and risk of developing one or more SC. Results: Among eligible patients, 847 were untreated, 243 were early ZA-treated and 218 were late ZA-treated. For untreated versus early ZA-treated groups, median FUP was 263 versus 357 days (p<0.0001), respectively, and time to first SC was 199 versus 273 days (p<0.0001), respectively. ZA treatment was associated with significantly longer FUP and lower SC risk. The early ZA-treated group had significantly longer FUP versus the late ZA-treated group (median days, 357 vs. 299.5); the late ZA-treated group experienced significantly higher SC risk vs. the early ZA-treated group (odds ratio, 1.51). Compared with the long-persistence group, FUP was 56 and 40 shorter in the short and medium groups, respectively (p<0.0001). Conclusion: Treatment with and early initiation of ZA for patients with prostate cancer and bone metastasis significantly prolonged time to and reduced risk of developing SC, while extending FUP.
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