Stable or at least once HER2-low status during neoadjuvant chemotherapy confers survival benefit in patients with breast cancer

Background: Temporal heterogeneity in human epidermal growth factor receptor 2 (HER2) status may be associated with the prognosis of breast cancer. We aimed to clarify the relationship of HER2-low transition during neoadjuvant therapy with survival outcomes under the new classification of HER2 status. Methods: This retrospective study was conducted based on the prospective database of breast cancer patients treated with neoadjuvant therapy from September 2013 to August 2020. Results: This analysis enrolled 185 patients, including 44 patients with HER2-zero tumours, 93 patients with HER2-low tumours and 48 patients with HER2-positive tumours after neoadjuvant therapy. Nearly, 57.6% of HER2-zero tumours turned into HER2-low tumours after neoadjuvant therapy, while 25.0% of HER2-low patients changed to HER2-zero or HER2-positive tumours. We found that at least once diagnosis as HER2-low breast cancer was related to hormone receptor status (p < .001) and Ki-67 expression (p = .036). Patients ever diagnosed as HER2-low tumours had favourable clinicopathological features (less Ki-67 expression, lower pathological staging, etc.) as well as significantly better locoregional relapse-free survival (LRFS; p = .007) and overall survival (OS; p = .026) compared with those never exhibiting HER2-low expression. Furthermore, the 6-year OS rates were 94.2% (95% confidence interval (CI) 83.1-98.1), 88.7% (74.4-95.2) and 78.1% (65.4-86.6) for patients with stable, once and none HER2-low expression, respectively (adjusted HR, 0.514 [95%CI, 0.294-0.897], p = .019). Conclusions: Our study first indicated in patients across all expression levels of HER2 that stable or at least once HER2-low status may confer favourable attributes including less malignant biological behaviour and long-term survival benefit for breast cancer receiving neoadjuvant therapy.