RecruitingPhase 2Drug trialA Trial of Trastuzumab Rezetecan in Unresectable Locally Recurrent/Metastatic Breast CancerThe study is designed to compare the efficacy and safety of different dose groups of Trastuzumab Rezetecan or Trastuzumab Deruxtecan in patients with HR-positive, HER2-low unresectable locally recurrent/metastatic breast cancer. It will also exploratively evaluate the pharmacokinetic profile and immunogenicity of Trastuzumab Rezetecan.