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

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).

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.

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%).

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.