RESUMEN
Objective: This study aimed to comprehensively analyze and compare the clinicopathological features and prognosis of Chinese patients with human epidermal growth factor receptor 2 (HER2)-low early breast cancer (BC) and HER2-IHC0 BC. Methods: Patients diagnosed with HER2-negative BC ( N = 999) at our institution between January 2011 and December 2015 formed our study population. Clinicopathological characteristics, association between estrogen receptor (ER) expression and HER2-low, and evolution of HER2 immunohistochemical (IHC) score were assessed. Kaplan-Meier method and log-rank test were used to compare the long-term survival outcomes (5-year follow-up) between the HER2-IHC0 and HER2-low groups. Results: HER2-low BC group tended to demonstrate high expression of ER and more progesterone receptor (PgR) positivity than HER2-IHC0 BC group ( P < 0.001). The rate of HER2-low status increased with increasing ER expression levels (Mantel-Haenszel χ 2 test, P < 0.001, Pearson's R = 0.159, P < 0.001). Survival analysis revealed a significantly longer overall survival (OS) in HER2-low BC group than in HER2-IHC0 group ( P = 0.007) in the whole cohort and the hormone receptor (HR)-negative group. There were no significant differences between the two groups in terms of disease-free survival (DFS). The discordance rate of HER2 IHC scores between primary and metastatic sites was 36.84%. Conclusion: HER2-low BC may not be regarded as a unique BC group in this population-based study due to similar clinicopathological features and prognostic roles.