Abstract P5-05-14: Real-World Treatment Patterns and Clinical Outcomes of Inetetamab combined with pyrotinib plus chemotherapy in Her-2 negative metastatic breast cancer patients : a multi-center retrospective study

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Abstract Background: Inetetamab is an innovative anti-HER2 monoclonal antibody. Studies indicated that the combination of the use of dual anti-HER2 components with complementary mechanisms of action will improve anti-tumor effect. The study aims to investigate the efficacy and safety of inetetamab combined with pyrotinib plus chemotherapy for HER2 positive metastatic breast cancer (HER2+MBC). Methods: From July 2020 to December 2022, 99 HER2+MBC patients received at least two cycles of inetetamab combined with pyrotinib plus chemotherapy treatment regimens in in multicenters in China. Data cut-off April 2023. The primary endpoint was progression-free survival (PFS), secondary endpoints were objective response rate (ORR) and safety. Results: In the overall population, the median PFS was 12.3 months (95% CI: 10.9-13.6), the ORR was 53.5%. Of the 99 patients in this cohort, 47(47.5%) patients received this treatment as first line (First-line subgroup) and 52(52.5%)patients as second line (Second -line subgroup) , respectively. The median PFS in the first-line subgroup was significantly longer than that in the second-line subgroup (15.0 months [95% CI: 13.6-15.8] vs. 10.3 months [95% CI: 9.6-10.9], p<0.001). In First-line subgroup, the combination regimen of albumin-bound paclitaxel provided longer median PFS than other chemotherapy (15.0 months [95% CI: 13.6-NA] vs. 11.1 months [95% CI: 8.6-NA], p=0.012). In addition, the study included 19 patients with brain metastases. The mPFS of patients with versus patients without brain metastases was 10.5 (95% CI: 9.5-12.9) months versus 13.0 (95% CI: 11.2-15.0) months (p= 0.052). 4 patients with brain metastases in the first-line subgroup had longer mPFS of 15.6 (95% CI: 10.0-NA) months. The most common grade ≥3 treatment-related adverse events observed were leukopenia (19.2%), diarrhea (18.2%), myelosuppression (7.1%) and neutromenia (4.0%). Conclusions: This study shows that Inetetamab combined with pyrotinib plus albumin-bound paclitaxel might be a safety and promising therapy for HER2-positive MBC, Including patients with brain metastases. Citation Format: Huanhuan Zhou, Chao Deng, Lu Gan, Fan Li, Xuefeng Xu, Yanman Fang, Xiaowei Qi, Weigang Bian, Zeshun Yu, Zhanhong Chen, Xiaojia Wang. Real-World Treatment Patterns and Clinical Outcomes of Inetetamab combined with pyrotinib plus chemotherapy in Her-2 negative metastatic breast cancer patients : a multi-center retrospective study [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 P5-05-14.

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