Association Between HER2 Status and pCR Rate in ER-positive Breast Cancer Receiving Neoadjuvant Endocrine or Chemotherapy

In estrogen receptor (ER)-positive breast cancer (BC), human epidermal growth factor receptor-2 (HER2)-low ones are reported to have distinct clinical and molecular features from those with HER2-zero or HER2-positive status. However, the association between HER2-low status with response to endocrine therapy is largely unknown. In this study, we included 518 ER-positive BC patients who received either neoadjuvant endocrine therapy (NET) or neoadjuvant chemotherapy (NCT). The pathologic complete response rate (pCR) of HER2-low and HER2-zero tumors re-sponding to neoadjuvant therapies were compared. The difference in disease-free survival (DFS) and overall survival (OS) between the two groups was also analyzed. The pCR (defined as ypT0/isNx) in HER2-low BCs and in HER2-zero BCs for NET cohort and NCT cohort were compared.