SHR-A1811 Monotherapy or Sequential THPy as Neoadjuvant Therapy for Stage II-III HER2-Positive Breast Cancer

This is a prospective, open-label, phase II, multicenter exploratory clinical study. Eligible female patients aged 18-75 years with stage II-III HER2-positive breast cancer will receive 4 cycles of SHR-A1811 (4.8 mg/kg, intravenous infusion every 3 weeks). After 4 cycles, tumor response will be assessed per RECIST 1.1 criteria. Patients with a ≥50% reduction in tumor burden will continue with another 4 cycles of SHR-A1811 followed by definitive surgery. Patients with \<50% reduction will receive 4 cycles of the THPy regimen (docetaxel + trastuzumab + pyrotinib) before surgery. Circulating tumor DNA (ctDNA) will be assessed for minimal residual disease (MRD) at baseline, after 4 cycles of treatment, and postoperatively. The primary endpoint is total pathological complete response (tpCR), assessed by an independent review committee (IRC). This study aims to evaluate the efficacy, safety, and feasibility of imaging- and MRD-guided neoadjuvant therapy in HER2-positive breast cancer.