A phase 3 trial of trastuzumab rezetecan (SHR-A1811) in HER2-low advanced breast cancer showed a substantial progression-free survival (PFS) improvement versus physician’s choice chemotherapy. Results from the HORIZON-Breast06 study were presented at the ESMO Congress 2026 and published simultaneously in JAMA. In chemotherapy-naïve patients, median PFS more than doubled to 16.6 months versus 6.8 months with chemotherapy (hazard ratio [HR] 0.25; 95% CI 0.19–0.33; P<.001). The benefit was consistent in the overall population as well, with a median PFS of 16.4 months versus 6.8 months (HR 0.27; 95% CI 0.21–0.34; P<.001). Subgroup analyses favored trastuzumab rezetecan across prespecified categories, with overall survival data still immature and described as showing a trend toward benefit. Investigators noted that direct head-to-head comparisons versus other approved HER2-low ADCs were not provided in these results.