Low Bone Mass

This is a randomized, double-blind, placebo- and active-controlled Phase II study evaluating the efficacy and safety of TST002 injection (a humanized monoclonal antibody) in postmenopausal women with osteoporosis or low bone mass, aged 45-80 years. Approximately 110 participants will be randomized 1:1:1:1:1 (stratified by baseline BMD T-score) to one of five arms: TST002 400 mg every 8 weeks (Q8W), TST002 800 mg Q8W, TST002 1200 mg every 12 weeks (Q12W), placebo, or open-label denosumab 60 mg subcutaneously every 24 weeks. The study includes a screening period (Day -28 to Day -1), a main study period (Week 0-24), and an extension period (Week 25-52), with all participants followed through Week 52 (Day 365). The primary objective is to evaluate the effect of repeated IV TST002 infusions on lumbar spine bone mineral density (BMD). Secondary objectives include characterization of pharmacokinetics, pharmacodynamics, immunogenicity, safety, and tolerability.