This study is designed to evaluate whether earlier treatment with zoledronic acid will further decrease the risk of skeletal related events. This is a randomized, double-blind, placebo-controlled, multicenter study followed by an open-label study. Patients are stratified according to ECOG performance status (0-1 vs 2), prior skeletal-related event (no vs yes), and serum alkaline phosphatase (< upper limit of normal [ULN] vs ≥ ULN).