267 Background: Denosumab, compared with ZA, has recently demonstrated significant benefits in preventing skeletal-related events (SREs) in a double-blind phase 3 study of men with castration-resistant PC and bone metastases (N=1901). This post hoc analysis was performed to determine if key bone metabolism biomarker levels correlated with time-to-first SRE. Methods: Time-to-Grade ≥2 increase in total serum alkaline phosphatase (ALP) was assessed for correlation with time-to-first SRE. Levels of urinary N-telopeptide (uNTX) and serum bone-specific alkaline phosphatase (BSAP) markers were measured at baseline and study week 13, and correlations with time-to-first SRE were assessed. Covariate analyses were performed using a Cox proportional hazards model, stratified by treatment group or (for baseline analyses) with treatment group as the independent variable. Results: Analysis of the relationship between time-to-Grade ≥2 increase in total ALP and time-to-first SRE demonstrated that Grade ≥2 increases in ALP of PC patients were associated with a higher risk of first SRE (hazard ratio [HR] 1.838, 95% confidence interval [CI] 1.559, 2.167; P<0.0001). In dichotomized analyses (< vs ≥ median), a higher level of uNTX and BSAP (at baseline or week 13) was correlated with an increased risk of first SRE (Table). In baseline covariate analyses, treatment benefit for denosumab was maintained after adjusting for either baseline uNTX (HR 0.818, 95% CI 0.703, 0.951; P=0.0091) or BSAP (HR 0.813, 95% CI 0.700, 0.943; P=0.0061). Conclusions: Higher levels of uNTX or BSAP at baseline or week 13 were associated with worse SRE outcomes in men with advanced PC and bone metastases. Denosumab was more efficacious for preventing or delaying SREs compared with ZA, regardless of bone-related biomarker levels. Relationship of covariate to time-to-first SRE Clinical trial information: NCT00321620. [Table: see text]
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