Comparative survival analysis of patients with HER2-low and HER2-positive metastatic breast cancer with or without brain metastases treated with trastuzumab deruxtecan.

Abstract

1036 Background: Breast cancer outcomes vary among HER2-amplified and HER2 low-expression patients, particularly in the presence of brain metastases (BM). Trastuzumab deruxtecan (T-DXd) is FDA approved for the treatment of adult patients with unresectable or metastatic human epidermal growth factor receptor 2 (HER2)-low and HER2-positive (HER2+) patients (pts). This study aims to evaluate the impact of T-DXd treatment on overall survival among HER2 low and HER2-positive metastatic breast cancer (MBC) patients with and without brain metastases (BM). Methods: A retrospective analysis was conducted by using de-identified data available from seven US-based health systems part of Guardian Research Network (GRN). Patients treated with T-DXd from December 2019 to December 2023 with a diagnosis of HER2 low (immunohistochemistry [IHC] 1 + or IHC 2+/negative with HER2 FISH non-amplified) and HER2+ (IHC 3+ or HER2+ and FISH amplified MBC were included. Median overall survival (mOS), calculated from the initiation of T-DXd treatment, was assessed using Kaplan-Meier Curve analysis and Log-rank test. Results: A total of 380 MBC pts were identified. Among these 231 (61.1%) were stratified as having HER2 low and 149 (38.9%) HER2+ MBC. Pts with HER2+ disease had a higher prevalence of BM (n=70; 47%) compared to HER2-low pts (n=55;23.8%). The median age at BM diagnosis was 60.5 years, range: 21.6 to 87.1 years. Within the entire BM group (n=125), there were more pts with ER+ disease (81.9%) in the HER2 low group compared to HER2+ group (55.8%, p=0.01). The majority of these patients had multiple prior lines of therapy. HER2+ BM pts had a median overall survival (mOS) of 9.3 months [CI: 6.79-11.88, log rank p <0.001], compared to 4.3 months [CI: 1.89-6.82, log rank p <0.001] in the HER2-low pts. Without BM, HER2+ pts had a mOS of 10.7 months [CI: 0.71-20.82, log rank p <0.001], compared to 6 months [CI: 3.47-8.67, log rank p <0.001] in the HER2-low pts. Conclusions: In this retrospective study of heavily pretreated MBC patients with multiple prior lines of therapy, pts with HER2+ MBC with and without BM had a longer mOS compared to those with HER2- low disease, suggesting HER2 expression as a key determinant of T-DXd efficacy. Poor survival in MBC patients without BM was attributed to pre-treatment with multiple lines of therapy. Future research should explore combination therapies and predictive biomarkers while conducting clinical trials to optimize treatment strategies for HER2+ metastatic breast cancer patients.