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

Inclusion Criteria: * Age ≥ 18 years. * For premenopausal and perimenopausal patients: negative pregnancy test and agreement to use reliable contraception during the treatment period. * Pathologically confirmed HER2-positive invasive breast cancer (IHC 3+ or IHC 2+ with FISH+). * Completed standard neoadjuvant TCbHP (taxane + carboplatin + trastuzumab + pertuzumab) with imaging assessment not achieving clinical complete remission (non-cCR). * Agree to undergo a core needle biopsy. * ECOG performance status 0 or 1. * Adequate organ function meeting the following criteria: hemoglobin ≥ 90 g/L, white blood cell count ≥ 3.5 × 10\^9/L, platelet count ≥ 100 × 10\^9/L, absolute neutrophil count ≥ 1.5 × 10\^9/L, AST/ALT ≤ 3 × ULN, total bilirubin ≤ 1.5 × ULN, serum creatinine ≤ 1.5 × ULN. * No myocardial ischemia on ECG; New York Heart Association (NYHA) functional class I; left ventricular ejection fraction (LVEF) ≥ 55% by echocardiography; cardiac troponin I (cTnI) and brain natriuretic peptide (BNP) within normal limits. * Signed informed consent. Exclusion Criteria: * Male breast cancer or inflammatory breast cancer. * Metastatic breast cancer (Stage IV). * Concurrent other malignancy or history of other malignancy within the past 5 years, except adequately treated basal cell or squamous cell skin cancer, or carcinoma in situ of the cervix. * Concurrent other anti-tumor therapy or participation in another clinical trial. * Severe non-malignant disease that would affect compliance or place the patient at risk. * Major surgery within 4 weeks prior to start of study treatment or anticipated need for major surgery during the study. History of allergic reaction or contraindication to any component of the study drug. * Dementia, mental abnormality, or any psychiatric illness that interferes with understanding of the informed consent. * Any other condition assessed by the investigator as unsuitable for inclusion.