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.

Inclusion Criteria:

patients diagnosed with invasive breast cancer and who received surgery from 2015 to 2021

Exclusion Criteria:

none

In this retrospective cohort study, we sourced data from the electronic database of Peking university cancer hospital to identify patients diagnosed with invasive breast cancer and who received surgery from 2015 to 2021. Patients were excluded by the fol-lowing criteria: (1) patients who were ER-negative; (2) patients who were HER2 posi-tive defined as IHC3+ or IHC2+/fluorescence in situ hybridization (FISH)-positive; (3) patients who were HER2 (IHC2+) but did not evaluate by further FISH;(4) patients who did not receive neoadjuvant therapy; (5) patients who received concurrent neo-adjuvant endocrine and chemotherapy. Patients who remained were further divided into two groups: those receiving neoadjuvant endocrine therapy (the NET group) and those receiving neoadjuvant chemotherapy (the NCT group).