Efficacy and safety of inetetamab-containing regimens in patients with HER2-positive metastatic breast cancer in first-line/second-line setting.

e13013 Background: Inetetamab is a novel recombinant humanized anti-human epidermal growth factor receptor-2 (HER-2) monoclonal antibody. This real-world retrospective study assessed the efficacy and safety of inetetamab-based combination regimens in first-line/second-line treatment of HER2-positive metastatic breast cancer (MBC). Methods: This study retrospectively recruited HER2-positive MBC patients who received inetetamab-based combination regimens from June 2020 to May 2023. The outcomes included progression-free survival (PFS), overall survival (OS), objective response rate (ORR), and disease control rate (DCR). Results: A total of 329 patients were enrolled and included in the efficacy analysis. The most frequently used treatment strategy was inetetamab plus pyrotinib-contained regimens (205/329, 62.3%). Patients treated with first-line regimens benefited the most, with a median PFS of 14.5 versus (vs.) 10.0 months (first-line- vs. second-line combination therapy of inetetamab, pyrotinib and chemotherapy, p <0.001), 18.0 vs. 17.0 months (first-line- vs. second-line combination therapy of inetetamab, pertuzumab and chemotherapy, p=0.096), and 14.0 vs. not applicable months (first-line- vs. second-line inetetamab plus chemotherapy, p=0.229). The complete response (CR) was observed in 14 (4.3%) patients. The ORR was 54.4% (95%CI, 49.0%-59.7%), and the DCR was 99.4% (95%CI, 97.8%-99.8%). Diarrhea (39.2%) and white blood cell count decreased (33.0%) were the most common adverse events (AEs). The grade 3 and higher AEs were observed in 29.5% of the whole study cohort. Conclusions: Inetetamab-based combinations therapy demonstrated promising clinical activity and a manageable safety profile in patients with HER2-positive MBC, especially in the first-line setting.