Trastuzumab rezetecan (SHR-A1811) improved progression-free survival versus physician’s choice chemotherapy in HER2-low advanced breast cancer in results from the Phase 3 HORIZON-Breast06 trial. The data were presented at the European Society for Medical Oncology (ESMO) Congress 2026 and published simultaneously in JAMA. The trial enrolled 551 patients with HER2-low advanced disease, including patients who had received no more than one prior line of chemotherapy for advanced cancer. In chemotherapy-naïve patients, median PFS rose to 16.6 months with trastuzumab rezetecan versus 6.8 months with physician’s choice (hazard ratio 0.25; P<.001). Benefit was also reported in the overall population, with median PFS of 16.4 months versus 6.8 months (hazard ratio 0.27; P<.001). Subgroup analyses indicated the PFS benefit was consistent across hormone receptor status. Overall survival data remained immature, but a trend favored the ADC. The report also noted that head-to-head comparative data versus already approved ADCs were not available at this stage, leaving uncertainty on where the regimen may land relative to therapies such as trastuzumab deruxtecan.