#ESMO2026 LBA13: Phase 3 HORIZON-Breast06 — Trastuzumab rezetecan (SHR-A1811) vs chemo in HER2-low advanced breast cancer.

HER2 ADC developed by 🇨🇳Hengrui.

Patients had received ≤1 prior line of chemo for metastatic disease (prior endocrine required for HR+).

551 patients randomized to SHR-A1811 6.4 mg/kg Q3W or physician’s choice chemo (taxanes, eribulin, capecitabine, or gemcitabine).

Key results (median follow-up 18.0 months):
• PFS (chemo-naïve): 16.6 vs 6.8 mo (HR 0.25, p<0.0001)
• PFS (overall): 16.4 vs 6.8 mo (HR 0.27, p<0.0001)
• Benefit consistent in HR+ and HR- subgroups
• OS immature but trend favors SHR-A1811
• ORR: ~76% vs ~43% (chemo-naïve); ~75.5% vs 41.2% overall

Safety: Grade ≥3 TRAEs 84.1% vs 67.9%. ILD reported in 7 patients (2.5%).