TDXD in Metastatic HER2-Positive Breast Cancer

Inclusion Criteria: * Female patients aged ≥ 18 years * Histologically confirmed HER2-positive metastatic breast cancer * Progression during or within 6 months of finishing adjuvant anti-HER2 therapy (T-DXd as 2nd line), OR de novo metastatic disease previously treated with ≥ 2 lines of anti-HER2 therapy (T-DXd as 3rd line or beyond) * ECOG Performance Status 0-1 * LVEF ≥ 50% on echocardiography * Measurable lesions per RECIST v1.1 * Adequate hematologic, hepatic, and renal function Exclusion Criteria: * History of non-infectious interstitial lung disease (ILD) / pneumonitis requiring steroids * Active uncontrolled infection * Symptomatic/uncontrolled brain metastases * Severe cardiac dysfunction (LVEF \< 50%) * Pregnancy or lactation