Clinicopathological Features and Prognostic Role of HER2 Low in Early Breast Cancer: A Real World Study

Purpose: A definition of human epidermal growth factor receptor-2 (HER2)-low was recently proposed with the development of novel antibody-drug conjugates (ADCs). Current studies on HER2-low are associated with metastatic breast cancer (BC), and less is known about early stage BC. Hence, a retrospective study was conducted based on HER2-low early BC to comprehensively analyze its clinicopathological features and prognostic roles compared with HER2 immunohistology(IHC) 0. Method: Patients with HER2-negative early BC (N = 999) diagnosed at our institution from January 2010 to December 2015 were enrolled in this study. We compared clinicopathological characteristics and survival outcomes, including disease-free survival (DFS) and overall survival (OS), between the HER2 IHC0 and HER2-low groups. Result: HER2-low BC accounts for 83.6% of the entire cohort, with a higher proportion of estrogen receptor (ER) levels (> 10 %) and progesterone receptor (PgR) positivity compared with HER2 IHC0. Survival analysis revealed a significantly longer OS in HER2-low BC than that of HER2 IHC0. Patients with HER2-low in the hormone receptor (HR)-positive group had longer OS than that of HER2 IHC0. A longer OS of HER2-low was also observed in HR-negative group. No significant differences were observed in the DFS. Conclusion: HER2-low BC may not be regarded as a unique BC group in this real-world population because of similar clinicopathological features and prognostic roles, especially in HR-positive cases. Whether HER2-low is a distinct subgroup remains to be supported and validated by additional data, both at the clinical and molecular levels.