Clinicopathologic Features and Prognosis of Female Early Breast Cancer With HER2 Low Expression: A Propensity Score Matched Analysis.

Background: Metastatic breast cancer (MBC) patients with low expression of human epidermal growth factor 2 (HER2) have been proven to benefit from HER2 targeted therapy. We aimed to determine how HER2-low status affected survival and metastatic risk as well as how it affected pathological complete response (pCR) in neoadjuvant chemotherapy (NAC) patients. Methods: According to the results of immunohistochemistry (IHC) and in situ hybridization (ISH) testing, 321 female patients were sorted into HER2-low (IHC 1+/2+ with ISH negative) and HER2-zero (IHC 0) groups using propensity score matching (PSM). Overall survival (OS), disease-free survival (DFS), and distant disease-free survival (DDFS) were compared for both groups, while pCR was only analyzed for NAC patients. Results: In total, 97 patients in each group after PSM were included. We discovered that pCR was not associated with HER2 expression status in 45 patients who underwent NAC. Five-year OS in the HER2-low group was significantly higher (98.99%) than in the HER2-zero group (95.87%, P = .044); however, this difference was not reflected in the 5-year DFS (90.61 vs 90.52%, P = .868) and 5-year DDFS (93.67 vs 91.53%, P = .757). Meanwhile, multivariate analysis revealed that HER2-low expression could indicate better OS (P = .047, hazard ratios [HRs] = 16.121, 95% confidence interval [CI] = 1.035-251.046), but it had no prognostic value for DFS or DDFS. Conclusion: When compared with HER2-zero expression, HER2-low expression was not connected to pCR and could not modify metastasis risk in female patients with early-stage breast cancer (BC), but it may prolong patient survival.