HORIZON-Breast06: Trastuzumab Rezetecan Reduces Progression Risk by 73% in HER2-Low Advanced Breast Cancer

Headline: HORIZON‑Breast06—trastuzumab rezetecan cuts progression risk by 73% in ERBB2‑low advanced breast cancer Updated phase III HORIZON‑Breast06 results presented at ESMO 2026 show trastuzumab rezetecan (SHR‑A1811) produced a large, clinically meaningful 73% reduction in risk of disease progression versus physician’s‑choice chemotherapy in patients with ERBB2 (HER2)‑low metastatic breast cancer. The magnitude of benefit suggests a potential practice change, but clinicians will be watching the drug’s adverse‑event profile closely when weighing efficacy against toxicity. Context: trastuzumab rezetecan is a third‑generation antibody–drug conjugate (ADCs) that uses a TOP1‑class payload and can exert a bystander effect, part of a broader wave of ADCs expanding into HER2‑low disease. (Sources: JAMA trial reports; OncoDaily ESMO coverage.)