Prognosis of patients with HER2-low breast cancer brain metastasis: A single-institution experience

e13109 Background: Many patients with breast cancer were reported to suffer from brain metastasis in the advanced setting. Traditionally, the HER2-low entity was classified as HER2-negative when evaluating prognosis and administrating treatment in patients with breast cancer brain metastasis (BCBM). Trastuzumab deruxtecan (T-DXd) was proved to have potent efficacy in HER2-low breast cancer, even with brain metastasis, which made this subtype a distinct entity. However, the evidence regarding HER2-low BCBM is scarce. Methods: Based on the clinical database of our institution, the BCBM patients with available HER2 status between January 2010 and July 2021 were selected. The enrolled patients with HER2 1/2+ in immunohistochemistry and negative for fluorescence in situ hybridization (FISH) were classified as HER2-low. The comparisons were conducted between HER2-low and HER2-zero category. We predefined the primary endpoint as the overall survival (OS) after the diagnosis of BCBM, which were further analyzed basing the status of hormone receptor (HR). The Kaplan–Meier curves with log-rank test and Cox proportional hazards model were utilized to analyze the survival outcomes. Results: A total of 272 cases were included in the database, among which the patients with HER2-zero (n=64) and HER2-low (n=71) subtypes were analyzed eventually. The OS of patients with HER2-low BCBM was better than the HER2-zero counterparts in the overall population (p=0.002) and the HR-negative group (p=0.008), while the similar tendency was not observed in the HR-positive patients. Moreover, the Cox regression analysis demonstrated that the HER2-low status was a significant prognostic factor for the better clinical outcome in the HR-negative patients (p=0.046 for multivariate analysis). Conclusions: The patients with HER2-low BCBM had better prognosis than the HER2-zero counterparts, especially in the HR-positive subgroup. The low expression of HER2 is supposed to be related to the long-term survival of BCBM patients.