A Study of RC48-ADC for the Treatment of Locally Advanced or Metastatic Breast Cancer With Low Expression of HER2

This study is a multi-center, randomized, open, parallel control to evaluate the effectiveness and safety of Phase III clinical trials of the efficacy and safety of recombinant humanized anti-HER2 monoclonal antibody-Monomethyl auristatin E (MMAE) conjugate for the treatment of locally advanced or metastatic breast cancer the study.The low expression of HER2 is defined as: the immunohistochemistry (IHC) confirmed by the central laboratory detects the expression of HER2 protein as IHC 2+ and the fluorescence in situ hybridization (FISH) detection has no amplification.