Clinical, Pathological Complete Response, and Prognosis Characteristics of HER2-Low Breast Cancer in the Neoadjuvant Chemotherapy Setting: A Retrospective Analysis

Background The present study was conducted to evaluate the clinical, pathological response, and prognosis characteristics of human epidermal growth factor receptor 2 (HER2)-low breast cancer in the neoadjuvant chemotherapy setting. Methods Patients with HER2-negative breast cancer who received neoadjuvant chemotherapy from January 2017 to December 2019 were retrospectively analyzed. HER2-negative breast cancer was divided into two groups: HER2-zero (defined as immunohistochemistry [IHC] 0) and HER2-low (defined as IHC 1+, or IHC 2+ and fluorescence in-situ hybridization-negative. Results Overall, 314 patients with HER2-negative breast cancer were analyzed. The proportion of HER2-low patients with hormone receptor (HR)-positive disease was higher than in triple-negative breast cancer (TNBC; 75.3% vs. 63.2%, p = 0.032). In HR-positive breast cancer, HER2-low tumors presented less nodal involvement (p = 0.023) and earlier clinical stage (p = 0.015) compared with HER2-zero tumors; however, in TNBC, HER2-low patients had a later clinical stage (p = 0.028). With the pathological complete response (pCR) defined as ypTis/0ypN0, there was no difference in pCR rates among the entire cohort, HR-positive disease, and TNBC. However, with the pCR defined as ypT0ypN0, the pCR rate in HER2-low breast cancer was significantly lower than HER2-zero breast cancer in the entire cohort (24.3% vs. 36.4%, p = 0.032) and the HR-positive subgroup (18.7% vs. 32.1%, p = 0.035), but not for TNBC. Multivariate analysis demonstrated that HER2 status (low vs. zero) was an independent predictive factor for pCR (p = 0.013) in HR-positive breast cancer. There were no statistically significant differences in 3-year disease-free survival and overall survival between HER2-low and HER2-zero breast cancer among the entire cohort, HR-positive disease, and TNBC. Conclusions HER2-low breast cancer exhibits specific clinical features and different response to treatment associated with HR status in the neoadjuvant chemotherapy setting.