Abstract Background: The management of human epidermal growth factor receptor 2-negative metastatic breast cancer (HER2-negative MBC) in second-line or later settings remains challenging due to the absence of standardized treatment regimens and the limited therapeutic efficacy of chemotherapy. Anlotinib, a novel multi-target tyrosine kinase inhibitor, exerts its effects by inhibiting angiogenesis. This study prospectively evaluated the efficacy and safety of anlotinib combined with chemotherapy as a second-line or later therapeutic option for HER2-negative MBC. Methods: Between August 2022 and August 2023, we prospectively enrolled 33 HER2-negative MBC patients who had experienced treatment failure following at least one line of systemic therapy in the metastatic setting. All participants received anlotinib in combination with chemotherapy. The primary endpoint was median progression-free survival (mPFS), while secondary endpoints included overall survival (OS), objective response rate (ORR), clinical benefit rate (CBR), disease control rate (DCR), and safety. Exploratory analyses utilized the Olink Target 96 Immuno-Oncology Panel to identify proteomic predictors of therapeutic response from serum samples collected from participants. Results: The cohort consisted of patients with hormone receptor-positive (HR+) /HER2-negative breast cancer (N=23) and triple-negative breast cancer (TNBC) (N=10). After a median follow-up duration of 25.9 months (95% CI: 19.9-32.0), the overall mPFS was 8.3 months, and the median OS was 22.2 months. In the HR+ and TNBC subgroups, mPFS was 7.4 months versus 10.6months, respectively. The ORR was 33.3%, DCR reached 90.9% and CBR stood at 60.6%. The analysis of Olink revealed that five proteins, namely CSF-1, VEGF, IL-6, IL-10, and IL-12, exhibited statistically significant differences between the sensitive and non-sensitive groups (P 0.05), and higher expression levels of these proteins experienced shorter PFS.Grade≥3 treatment- related adverse events were reported in 21.2% of patients including hypertriglyceridemia and neutropenia, with no treatment-related fatalities documented during the study period. Conclusion: Anlotinib combined with chemotherapy demonstrated promising efficacy and an acceptable safety profile for second-line or later treatment of patients with HER2-negative MBC. Baseline serum levels of VEGFA, CSF-1, IL-6, IL-10, and IL-12 identified through proteomic analysis show potential as predictive biomarkers for therapeutic response. These findings necessitate validation in larger randomized clinical trials. Citation Format: Y. Yuan, T. Xu, Q. Gu, L. Zhang, S. Li. Phase II Trial of Anlotinib-Chemotherapy Combination in HER2-Negative Metastatic Breast Cancer: Therapeutic Efficacy and Proteomic Biomarker Profiling abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-09-26.
Yuan et al. (Tue,) studied this question.