JSKN003

This study is a randomized controlled, open-label, multicenter phase III clinical study evaluating the efficacy and safety of chemotherapy selected by investigator JSKN003 s in subjects with recurrent or metastatic breast cancer who have previously failed first- or second-line chemotherapy in subjects with recurrent or metastatic breast cancer who have failed prior first- or second-line chemotherapy. The study planned to enroll 408 subjects in a 1:1 ratio and stratified block randomization method assigned to: * Experimental group: JSKN003 monotherapy * Control group: investigator's chosen chemotherapy drug (capecitabine, gemcitabine, vinorelbine, docetaxel, albumin-bound paclitaxel, or eribulin) monotherapy

This study is designed to compare the safety and efficacy of JSKN003 versus T-DM1 in unrespectable locally advanced and/or metastatic HER2-positive breast cancer participants previously treated with trastuzumab and taxane.

The purpose of this study is to establish a prospective, single-center platform research based on clinical subtypes to explore precision neoadjuvant therapy in patients with operable breast cancer who met the indications for neoadjuvant chemotherapy and by the update of basic translational research in the center, especially the refinement of typing, the discovery of new targets and the development of novel targeted drugs, verified the effectiveness of new targeted drugs in neoadjuvant therapy.