Abstract PO5-05-11: The effect of eribulin treatment for patients with HER2-low breast cancer

Abstract Background: Eribulin, a nontaxane, synthetic microtuble dynamics inhibitor, induces longer overall survival (OS) in patients with advanced or metastatic breast cancer (MBC). Interestingly, it also improves the tumor immune microenvironment via vascular remodeling. DESTINY-Breast04 trial showed that trastuzumab deruxtecan resulted in significantly longer OS of human epithelial growth receptor 2 (HER2)-low breast cancer patients, and this mechanism may also be related to tumor microenvironment. In this study, we investigated the effect of eribulin for patients with HER2-low breast cancer. Materials and Methods: This retrospective study comprised 97 MBC treated with eribulin from August 2011 to April 2019 at our institute. HER2 levels were determined through tumor biopsy specimen at first medical examination. We evaluated the correlations between HER2 levels and clinicopathological features, including the prognosis and immune related markers in each breast cancer subtype. We also classified the progressive disease (PD) into progression due to pre-existing lesion (PPL) and progression due to new metastasis (PNM) based on systemic computed tomography findings, and investigated the relationships between HER2 expression and PD types. Results: HER2-high group had significantly better OS than other groups (p=0.021, log-rank). Hormone receptor (HR)-negative/HER2-low patients had significantly better progression-free survival (PFS) than HR-negative/HER2-negative (p=0.024, log-rank). Though we also examined HER2 levels of recurrent tumor specimen, it was not a significantly useful prognostic marker in patients with HR-negative breast cancer (p=0.085, log-rank). There was no significant correlation between HER2 expression and any tested clinicopathological parameter, including absolute lymphocyte count, neutrophil-to-lymphocyte ratio and tumor infiltrating lymphocytes. PD were observed in 64 patients (PPL: n=47, PNM: n=17). PD type of all HR-positive/HER2-high patients was PNM, whereas all HR-negative/HER2-high patients was PPL (p=0.035). HER2-low group tended to have a higher PPL rare than negative group (83.3% vs 69.2%). Conclusions: In HR-negative/HER2-low group, PFS was improved by eribulin treatment, which might be due to unique anticancer effect of eribulin, suppression of epithelial-mesenchymal transition. Further study of this mechanism through basic research is important. Also, assessment of HER2 from primary tumor may be more useful than recurrent specimen. Citation Format: Wataru Goto, Saeko Henmi, Mariko Nishikawa, Asuka Kouchi, Rika Kouhashi, Akimichi Yabumoto, Koji Takada, Yuka Asano, Yukie Tauchi, Kana Ogisawa, Tamami Morisaki, Shinichiro Kashiwagi. The effect of eribulin treatment for patients with HER2-low breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-05-11.