Trastuzumab Rezetecan (T-DXh) in HER2+ Breast Cancer With Non-pCR After TCbHP

This is a prospective, multi-center, single-arm, phase 2 exploratory study to evaluate the efficacy and safety of adding 4 cycles of Trastuzumab Rezetecan (T-DXh), an anti-HER2 antibody-drug conjugate, as continued neoadjuvant therapy in patients with early or locally advanced HER2-positive breast cancer who have residual invasive disease after standard 6-cycle TCbHP (taxane, carboplatin, trastuzumab, pertuzumab) neoadjuvant therapy. Patients will receive 4 cycles of T-DXh (4.8 mg/kg IV Q3W) followed by radical surgery. The primary endpoint is tpCR rate. Secondary endpoints include ORR, EFS, OS, 3-year iDFS, and safety. Simon's two-stage design (H0: pCR ≤10%, H1: pCR ≥25%, α=0.05, β=0.2) requires 43 evaluable patients; with 10% dropout, 48 patients will be enrolled.