Abstract P5-03-14: Efficacy and safety of inetetamab-containing regimens in patients with HER2-positive metastatic breast cancer in first-line/second-line setting

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Abstract Inetetamab is a novel recombinant humanized anti-Human epidermal growth factor receptor 2 (HER2) monoclonal antibody. This real-world retrospective study assessed the efficacy and safety of inetetamab-containing regimens in first-line/second-line treatment of HER2-positive metastatic breast cancer (MBC). This study retrospectively recruited HER2-positive MBC patients who received inetetamab- containing regimens from June 2020 to May 2023. The outcomes included progression-free survival (PFS), objective response rate (ORR), and disease control rate (DCR). A total of 329 patients were enrolled and included in the efficacy analysis. The most frequently used treatment strategy was contained inetetamab plus pyrotinib (205/329, 62.3%). Of 329 patients for efficacy evaluation, the median PFS was 14.5 months. Patients treated with first-line regimens benefited the most, with a median PFS of 15.0 versus (vs.) 10.0 months (first-line- vs. second-line inetetamab plus pyrotinib, p <0.001), 19.0 vs. 17.0 months (first-line- vs. second-line inetetamab plus pertuzumab, p=0.096), and 14.0 vs. not reached months (first-line- vs. second-line inetetamab plus chemotherapy, p=0.229). The inetetamab plus pertuzumab group had the longest survival compared with inetetamab plus pyrotinib and inetetamab plus chemotherapy group in first-line (mPFS, 19.0 vs. 15.0 vs. 13.0 months) and second-line (mPFS, 17.0 vs. 10.0 vs. not reached months) settings. The ORR was 54.4% (95%CI, 49.0%-59.7%), with 14 (4.3%) complete response (CR) and 150 (45.6%) partial response (PR). Besides, 148 (45.0%) patients had stable disease (SD) for a disease control rate (DCR) of 99.4% (95%CI, 97.8%-99.8%). Grade 3 or higher adverse events (AEs) were observed in 29.5% of all 329 patients and mainly included diarrhea (38/329, 11.6%), white blood cell decreased (32/329, 9.7%), myelosuppression (18/329, 5.5%), neutrophil count decreased (7/329, 2.1%). No treatment-related deaths were reported. Compared with the other two subgroups, the incidence AEs of any grade (205/329, 62.3%) and grade ≥3 (80/329, 24.3%) in inetetamab plus pyrotinib group was the highest. Following the first- and second-line of treatment, inetetamab- containing combinations demonstrated promising clinical activity and a manageable safety profile in patients with HER2-positive MBC, especially in the first-line treatment. Citation Format: Yuxin Mu, Hui Zhang, Chao Deng, Jiao Yang, Lu Gan, Qingmo Yang, Xuefeng Xu, Wanping Liang, Xiaowei Qi, Liang Xu, Jian Zhang. Efficacy and safety of inetetamab-containing regimens in patients with HER2-positive metastatic breast cancer in first-line/second-line setting [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P5-03-14.

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