Real-world efficacy and safety of inetetamab-based therapy in patients with HER2-positive metastatic breast cancer with prior trastuzumab exposure: A multi-center retrospective study.

e13007 Background: Inetetamab is a novel recombinant humanized anti-HER2 monoclonal antibody (mAb). There was still no direct data with large sample sizes to evaluate the efficacy of inetetamab-based therapy in HER2-positive metastatic breast cancer patients who had previously received trastuzumab treatment. This study aimed to observe the larger-scale real-world efficacy and safety of inetetamab, analyze the characteristics of the benefit population and explore more excellent treatment choices. Methods: A multicenter retrospective real-world study which collected the clinicopathological data of HER2-positive metastatic breast cancer patients treated with inetetamab in multicenters in China. The progression-free survival (PFS), objective response rate (ORR) and disease control rate (DCR) of patients who received inetetamab therapy were estimated. Adverse events (AEs) were classified based on the Common Toxicity Criteria established by the National Cancer Institute. Results: A total of 500 patients were included in the final analysis according to the established inclusion criteria. The median PFS was 7 months in the overall cohort. The median number of treatment lines administered was three. The ORR was 28.6%, and the DCR was 89.2%. Meanwhile, patients who received a combination treatment of inetetamab, tyrosine kinase inhibitors (TKIs) and chemotherapy achieved the most prolonged PFS of 9.0 months and the higher ORR of 29.3%. The most common treatment-related AEs were neutropenia (36.4%) and leukopenia (31.4%), which were generally well-tolerated. Conclusions: Inetetamab demonstrated promising efficacy and safety in HER2-positive metastatic breast cancer patients who had prior exposure to trastuzumab, particularly in combination with TKIs and chemotherapy. Further research and comparative analysis should be necessary for therapeutic benefits.