New insights into HER2-low breast cancer brain metastasis: A retrospective analysis

Background: A considerable number of patients with breast cancer will suffer from brain metastasis in the advanced setting. The HER2 status serves as a significant prognostic factor and the reference of applying treatment for patients with breast cancer brain metastasis (BCBM). Methods: Between January 2010 and July 2021, patients with BCBM who had available HER2 status were identified. The patients with HER2 1+ in immunohistochemistry (IHC) or IHC 2+ and fluorescence in situ hybridization (FISH) negative were categorized as HER2-low. Comparisons were conducted between the HER2-low and HER2-zero population. The primary endpoint was overall survival (OS) after the diagnosis of BCBM. Survival outcomes were assessed using Kaplan -Meier curves with log -rank test and Cox proportional hazards model. Results: In this study, we analyzed 71 patients with the HER2-low breast cancer subtype and 64 patients with the HER2-zero subtype. Despite the limited sample size, our findings revealed a significantly better OS for patients with HER2-low cancer compared to their HER2-zero counterparts (26 m vs 20 m, p = 0.0017). This trend was particularly notable in the HR -negative group (26 m vs 13 m, p = 0.0078), whereas no significant difference was observed among the HR -positive patients. Furthermore, Cox regression analysis revealed that the HER2-low status was an independent prognostic factor for better survival in the HR -negative patients (p = 0.046 in multivariate analysis). Conclusions: Patients diagnosed with HER2-low BCBM exhibited a more favorable prognosis than those with HER2-zero BCBM, particularly within the HR -negative subgroup. The low expression of HER2 is supposed to be linked to the prolonged survival of BCBM patients.