Molecular characteristics and prognosis of breast cancer patients with different level of HER2 positivity after adjuvant and neoadjuvant chemotherapy

Purpose HER2-low breast cancer (BC) has renewed interests of researchers worldwide. Here, we aimed to investigate the clinicopathological characteristics of patients with HER2-low, HER2-0 and HER2 ultra-low BC and make conclusion. Methods We collected cases of patients who were diagnosed as BC at Jingling General hospital. Immunohistochemistry was used to redefine HER2 scores. Kaplan–Meier methods and Cox proportional hazards regression analysis were used to compare survival. Results We found that HER2-low BC was more frequent in hormone receptor (HR)–positive BC patients and was associated with fewer T3-T4, lower breast conserving surgery rate and higher adjuvant chemotherapy rate. HER2-low BC patients had better overall survival (OS) compared to HER2-0 BC in premenopausal and stage II BC. Furthermore, HER2-0 BC patients had lower Ki-67 expression levels compared to HER2-ultra low and HER2-low BC in HR–negative BC. HER2-0 BC patients also had worse OS rate compared to those with HER2-ultra low BC in HR–positive BC. Finally, HER2-0 BC patients showed a higher pathological response rate compared to those with HER2-low BC after neoadjuvant chemotherapy. Conclusions These findings suggest that HER2-low BC has distinct biology and clinical features compared to HER2-0 BC, and more investigation is needed to understand the biology of HER2-ultra low BC.