Real-World Outcomes With Inetetamab-Based Regimens for HER2-Positive Metastatic Breast Cancer: A Multicenter Retrospective Analysis in China

Introduction Inetetamab has demonstrated favorable efficacy and safety in treating HER2-positive metastatic breast cancer (MBC). Methods The multicenter retrospective study enrolled 140 patients with HER2-positive MBC who received inetetamab-based regimens between November 2020 and April 2023. Primary endpoint was progression-free survival (PFS); secondary endpoints included objective response rate (ORR), disease control rate (DCR), and safety. Results The median patient age was 53 (range: 27-90) years, with inetetamab-based regimens administered as first-, second-, or third-line (or later) therapy in 13 (9.3%), 29 (20.7%), and 98 (70.0%) patients, respectively. Median PFS was 6.1 months in the overall population, with an ORR of 35.0% and a DCR of 77.1%. Patients receiving inetetamab as first- or second-line therapy had significantly longer median PFS (14.5 months; 95% CI, 9.5-19.5) than those receiving it as third-line or later therapy (4.8 months; 95% CI, 4.2-5.3; P < 0.0001). First-line treatment resulted in a median PFS of 22.2 months. Patients previously treated with trastuzumab without HER2-TKIs had longer median PFS than those with prior TKI exposure (12.8 vs 5.7 months; P = 0.001). Multivariate analysis confirmed that treatment line (1-2 vs ≥3) was independently associated with PFS (hazard ratio = 0.330; 95% CI: 0.211-0.517). The most common grade 3 or 4 adverse events included leukopenia (16.4%) and neutropenia (12.9%). No treatment-related deaths were reported. Conclusion Inetetamab-based regimens have shown promising efficacy and are well-tolerated for patients with HER2-positive MBC. These anti-HER2 regimens could be considered an alternative treatment option for this disease.