Abstract
BACKGROUND: Breast cancer remains a leading cause of morbidity and mortality among women worldwide, with significant geographic disparities in its impact. While human epidermal growth factor receptor 2 (HER2)-targeted therapies, such as trastuzumab, have improved outcomes for HER2-positive breast cancer, challenges like therapy resistance persist, highlighting the need for novel treatments. Recent developments in antibody-drug conjugates (ADCs), particularly disitamab vedotin (RC48), show promising efficacy in targeting both HER2-positive and HER2-low expression tumors, warranting further investigation through real-world studies to assess its broader clinical applicability. METHOD: This retrospective, multicenter observational study evaluated the real-world efficacy and safety of RC48 in patients with HER2-positive or HER2-low breast cancer across three medical centers in China. Patient demographic characteristics, treatment patterns, sequential use of ADCs, and treatment-related adverse events were recorded and analyzed. RESULT: The median progression-free survival (mPFS) for the overall population (n = 96) was 4.31 months, with HER2-positive patients demonstrating significantly longer mPFS (5.26 months) compared to HER2-low patients (3.45 months; p = 0.044), while subgroup analyses revealed no significant differences in mPFS based on estrogen receptor (ER), progesterone receptor (PR), or hormone receptor (HR) status. Safety data indicated that adverse events were consistent with prior reports, with no new safety concerns identified during the study period. CONCLUSION: This real-world study demonstrates the efficacy of RC48 in both HER2-positive and HER2-low breast cancer. Notably, combination therapy significantly improved outcomes in HER2-low patients.