Sequencing SG vs. T-DXd in HER2-Low/TROP2-High Metastatic Breast Cancer

Currently, no phase III RCT has directly compared SG and T-DXd sequencing strategies, and the predictive role of biomarkers remains unclear. Additionally, there is no standard scoring system for Trop-2 expression. The ASCENT trial utilized an H-score method (H-score = 3×%IHC3+ + 2×%IHC2+ + 1×%IHC1+), with scores \200 defining low, medium, and high Trop-2 expression, respectively.This prospective study aims to: 1) Evaluate the efficacy of SG vs. T-DXd in HER2-low/Trop-2-high metastatic breast cancer, prioritizing SG for Trop-2-high patients and T-DXd for others. 2) Compare sequential treatment outcomes-T-DXd after SG failure versus SG after T-DXd failure-to inform ADC sequencing in HER2-low disease. Up to one intervening therapy is allowed before sequencing. 3) Identify biomarkers of ADC efficacy and resistance through quantitative protein analysis to optimize patient selection.