Inetetamab-based therapy in real-world treatment patterns with HER2-positive advanced breast cancer patients: a retrospective single-center study.

Background Inetetamab is a novel antibody targeting human epidermal growth factor receptor 2 (HER2) developed in China. Due to its optimized antibody-dependent cell-mediated cytotoxicity effect compared with trastuzumab, it has shown good efficacy and safety in the treatment of HER2-positive advanced breast cancer (ABC). Objectives This study aimed to investigate the efficacy and safety of inetetamab combination therapy in the treatment of HER2-positive ABC in real-world clinical practice. Design Retrospective study. Methods A total of 133 patients with HER2-positive ABC who were treated with inetetamab-based regimens between March 2020 and January 2024 were retrospectively included in this study. The main endpoint was median progression-free survival (mPFS). The secondary endpoints included objective response rate (ORR), disease control rate (DCR), and safety. Results The study included 133 HER2-positive ABC patients, and the median age was 55 years. The mPFS was 8.0 (6.7-9.3) months. The ORR was 50.4%, while the DCR was 88.7%. The mPFS for patients receiving inetetamab-based therapy as first to second, third to fourth, and later lines of metastatic treatment were 14.0, 7.0, and 6.0 months, respectively. Patients treated with inetetamab plus pyrotinib plus chemotherapy, especially with capecitabine, had the best outcomes (mPFS = 14.0 months). Multivariate analysis revealed that prior HER2-TKI treatment was significantly associated with worse PFS (hazard ratios 2.829, 95% confidence interval 1.265-6.328, p = 0.011). Subgroup analysis indicated that patients without visceral metastases had significantly better PFS (14.0 months vs 8.0 months, p = 0.003). The overall incidence of any grade adverse events (AEs) was 100%, with most being grades 1-2. Severe complications included neutropenia (37.6%) and leukopenia (33.1%). Conclusions Inetetamab-based combination therapy shows promising efficacy and good safety in patients with HER2-positive ABC. It is one of the late-line treatment options for Chinese patients with HER2-positive ABC.