Trastuzumab rezetecan (SHR-A1811) produced a substantial progression-free survival benefit versus physician’s choice chemotherapy in HER2-low advanced breast cancer in the phase 3 HORIZON-Breast06 trial. Results were presented at the European Society for Medical Oncology (ESMO) Congress 2026 and published in JAMA. In chemotherapy-naïve patients (551 total enrolled), median PFS more than doubled to 16.6 months with the ADC versus 6.8 months with control (hazard ratio 0.25). The benefit was consistent across hormone receptor status groups, with the median PFS in the overall population at 16.4 months versus 6.8 months (HR 0.27), while overall survival data remained immature. Journals and conference reporting also note that head-to-head comparisons against already-approved ADCs were not available in the trial, leaving comparative positioning to future studies.