Comparison of clinicopathological characteristics and response to neoadjuvant chemotherapy between HER2-low and HER2-zero breast cancer.

Novel anti-HER2 antibody-drug conjugates trastuzumab deruxtecan (DS-8201a) showed its effect in previously-treated HER2-low metastatic breast cancer, suggesting a promising future in HER2-low breast cancer. We retrospectively reviewed the clinicopathological data of 325 patients with stage I-III HER2 negative breast cancer who received neoadjuvant chemotherapy in the First Affiliated Hospital of Sun Yat-sen University from January 2016 to June 2021. In general, 91 patients (28.0%) were HER2-zero, and 234 patients (72.0%) were HER2-low. The pathological complete response (pCR) rate of the entire cohort was 17.3%. The pCR rate was 16.7% in HER2-low group, and 18.9% in HER2-zero group, showing no significant difference. Patients with HER2-low tumors had significantly longer overall survival (OS) than patients with HER2-zero tumors. ER status was the affecting factor of OS in HER2-low patients in both univariate and multivariate analysis. In conclusion, evidence for HER2-low BC as a distinct entity is insufficient, and more efforts are needed to standardize the scoring of HER2-low breast cancer.