RC48-ADC in HER2-low Advanced Breast Cancer

Inclusion Criteria: * Female patients aged ≥18 years * Expected survival ≥12 weeks * ECOG 0-1 * Histologically confirmed invasive advanced or metastatic breast cancer that is incurable and unresectable * At least one measurable lesion according to the RECIST 1.1 * No history of antibody-drug conjugate use * Up to one previous chemotherapy for advanced disease * Available hormone receptor status. Hormone receptor-positive subjects are allowed to receive no more than two previous endocrine therapy for advanced disease * HER2-low tumors, defined as IHC1+ or IHC2+ with negative FISH test; or HER2-ultralow tumors, defined as incomplete and faint membrane staining in \>0 but ≤10% of tumor cells * Adequate organ function Exclusion Criteria: * History of thromboembolic events * Uncontrolled systemic diseases, including diabetes, hypertension, interstitial lung disease, cirrhosis, etc. * Active infections requiring systemic treatment * Pregnant or lactating * Presence of brain metastases and/or carcinomatous meningitis