Inetetamab-Based Regimens for Patients with HER2-Positive Metastatic Breast Cancer: A Real-World Retrospective Study

Liping Chen, Jiayi Huang, Xuelian Chen, Xiaofeng Lan, Lin Song, Xiaofeng Xie, Xue Bai, Caiwen Du Department of Medical Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, Guangdong, People’s Republic of ChinaCorrespondence: Caiwen Du, Email [email protected]: Inetetamab is a Chinese-origin recombinant anti-HER2 monoclonal antibody. Herein, we assessed the efficacy and safety of inetetamab-containing regimens in patients with HER2-positive metastatic breast cancer (MBC).Patients and Methods: We retrospectively reviewed the medical records of patients with HER2-positive MBC who received inetetamab-containing regimens as a salvage treatment in metastatic setting from December 2020 to April 2024. The primary endpoint was progression-free survival (PFS) in the total population (TP). Patients with brain metastases were also included. Secondary endpoints were objective response rate (ORR), disease control rate (DCR), and safety.Results: At the data cut-off date of June 1, 2024, a total of 90 patients were included in this analysis. Median follow-up duration was 7.2 months (IQR 3.6– 13.1). The median PFS was 12.0 months (95% confidence interval [CI] 7.3 to 17.0 months) in the TP. The median PFS in the subgroup with brain metastases reached 10.0 months (95% CI 5.9 to NA months). The ORR was 46.6% (42/90), and the DCR was 92.2% (83/90). The most frequently combined chemotherapy was vinorelbine (83/90,92.2%). The most frequently concomitant targeted drug was pyrotinib (70/90,77.8%). The median PFS not reached for first-line, 15.9 months (95% CI 11.9 to NA months) for second-line, and 5.9 months (95% CI 4.4 to 12.2 months) for third-line or later therapy. Cox univariate and multivariate analyses demonstrated that lines of treatment were the only significant predictive factor for PFS (first- and second-line vs third-line or above: 15.9 vs 5.9 months, p=0.0021). The toxicity was tolerable. The most frequent grade 3 or 4 treatment-related adverse events were diarrhea (12.2%).Conclusion: Inetetamab offers a promising option and a manageable safety profile for HER2-positive MBC who pretreated with multiple-line therapies. Meanwhile, inetetamab plus small-molecule TKIs regimens shows good anti-tumor efficacy for MBC with brain metastases, which deserves further validation in a larger group trial.Keywords: inetetamab, HER2-positive metastatic breast cancer, pretreated, safety