BACKGROUND

ESG401 is a further optimized antibody-drug conjugate comprising a humanized anti-trophoblast cell-surface antigen 2 immunoglobulin G1 monoclonal antibody conjugated to SN-38, a topoisomerase I inhibitor, via a proprietary novel stable linker. The analysis aimed to explore the efficacy of ESG401 in human epidermal growth factor receptor 2 (HER2)-negative breast cancer (BC) patients with brain metastases (BMs), a population urging significant clinical need with limited systematic treatment options.

PATIENTS AND METHODS

This subgroup analysis was conducted as part of an open-label, multi-dose, dose-escalation, and cohort-expansion multicenter phase I trial. Eligible participants were aged 18-75 years and had locally advanced or metastatic solid tumors. For this subgroup analysis, patients with histologically confirmed HER2-negative BC and BMs were enrolled. Efficacy endpoints included overall objective response rate (ORR), disease control rate (DCR), and progression-free survival (PFS). Intracranial-specific endpoints included intracranial ORR (iORR), intracranial DCR (iDCR), and intracranial PFS. This trial is registered at ClinicalTrials.gov, NCT04892342.

RESULTS

Among 17 patients with efficacy-evaluable BMs, the iORR was 41% (7/17) [95% confidence interval (CI) 18.4% to 67.1%] including 3 patients achieving an intracranial complete response. The iDCR was 76% (13/17) (95% CI 50.1% to 93.2%). The overall ORR was 53% (9/17) (95% CI 27.8% to 77.0%), the overall DCR was 71% (12/17) (95% CI 44.0% to 89.7%), and the medium PFS was 5.7 months. The safety profile was consistent with previous reports.

CONCLUSIONS

These findings suggest that ESG401 is a promising and well-tolerated treatment option for BMs.