Low-Dose Apatinib Plus Chemotherapy in ADC-Pretreated HER2-Positive and HER2-Low Advanced Breast Cancer

This is a single-arm, open-label, phase 2 clinical trial using a stratified Simon minimax two-stage design. The study aims to evaluate the efficacy and safety of low-dose apatinib (250 mg daily) combined with physician-selected single-agent chemotherapy (TPC, capecitabine preferred) in patients with HER2-positive or HER2-low advanced/metastatic breast cancer who progressed after prior ADC therapy (T-DXd or SHR-A1811). Patients are stratified by HER2 status, HR status, lines of prior ADC therapy, and metastasis sites. Approximately 56 patients will be enrolled. The primary endpoint is objective response rate (ORR). Secondary endpoints include PFS1, PFS2, TTP, safety, and OS.