Neoadjuvant Regimens and Their Impact on Adjuvant T-DM1 Outcomes in HER2-Positive Early Breast Cancer

Background and Objectives: In early-stage HER2-positive breast cancer, ado-trastuzumab emtansine (T-DM1) has been adopted as the preferred adjuvant approach for patients left with residual invasive disease despite neoadjuvant therapy. The influence of different neoadjuvant regimens on subsequent outcomes in real-world settings remains uncertain. Materials and Methods: From 2019 to 2025, 102 patients treated with adjuvant T-DM1 following surgery after neoadjuvant chemotherapy were retrospectively assessed. Neoadjuvant regimens included doxorubicin plus cyclophosphamide followed by trastuzumab-paclitaxel, doxorubicin plus cyclophosphamide with pertuzumab-trastuzumab-docetaxel, or docetaxel-carboplatin-trastuzumab-pertuzumab. Clinical features, treatment response, survival, and toxicity were evaluated. Results: The mean age of the cohort was 49.7 years, and the majority of patients (80.4%) were aged 40 years or older. Hormone receptor positivity was 82.0%, and invasive ductal carcinoma accounted for 97.1% of cases. Regional responses included 39.2% with axillary pCR despite residual breast lesions, and 5.9% with breast pCR accompanied by axillary disease. Kaplan-Meier analysis demonstrated disease-free survival rates of 100%, 95.2%, and 92.2% at 1, 3, and 5 years, respectively. Adverse events were predominantly grade 1-2, while grade 3-4 toxicities occurred in under 5% of the cohort. Baseline characteristics varied across regimens, reflecting real-world treatment preferences, but survival outcomes remained comparable. Conclusions: Adjuvant T-DM1 was associated with high survival rates and manageable toxicity across different neoadjuvant regimens, underscoring its consistent benefit in routine clinical practice.