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Life sciences · Journal article
JAMA · October 23, 2026
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Importance Trastuzumab rezetecan (SHR-A1811) has demonstrated encouraging antitumor activity in a global phase 1 trial involving heavily pretreated patients with erythroblastic oncogene B (ERBB2)–low metastatic breast cancer. Objective To compare trastuzumab rezetecan vs physician’s choice of chemotherapy in patients with ERBB2-low metastatic breast cancer. Design, Setting, and Participants This open-label, randomized, multicenter phase 3 trial was conducted at 73 hospitals across China. Eligible patients were females aged 18 to 75 years with centrally confirmed ERBB2-low (immunohistochemistry [IHC] 1+ or IHC 2+/in-situ hybridization [ISH]–negative) unresectable locally recurrent or metastatic breast cancer who had received 1 or fewer prior lines of chemotherapy for metastatic disease, with prior endocrine therapy required for hormone receptor–positive disease. Enrollment began on June 30, 2023, and ended on August 20, 2025. The last day of follow-up for the final analysis for progression-free survival in the current study was March 20, 2026. Interventions Patients were randomly assigned (1:1) to receive trastuzumab rezetecan (6.4 mg/kg intravenously every 3 weeks; n = 277) or physician’s choice of chemotherapy (n = 274). Main Outcomes and Measures The primary end point was progression-free survival assessed by blinded independent central review in chemotherapy-naive patients and the overall population. Results Between June 30, 2023, and August 20, 2025, a total of 551 patients were randomized, with a mean (SD) age of 54.9 (9.9) years. At the data cutoff (March 20, 2026), trastuzumab rezetecan significantly prolonged progression-free survival compared with chemotherapy in the chemotherapy-naive patients (median, 16.6 [95% CI, 14.0-19.4] months vs 6.8 [95% CI, 5.7-7.0] months; hazard ratio, 0.25 [95% CI, 0.19-0.33]; P <.001) and the overall population (median, 16.4 [95% CI, 14.0-16.8] months vs 6.8 [95% CI, 5.7-6.9] months; hazard ratio, 0.27 [95% CI, 0.21-0.34]; P <.001). The benefit was consistent in hormone receptor–negative disease (median progression-free survival: 16.5 vs 6.8 months; hazard ratio, 0.34, [95% CI, 0.22-0.54]) and hormone receptor–positive disease (median progression-free survival: 16.4 vs 6.7 months; hazard ratio, 0.24 [95% CI, 0.18-0.33]). Grade 3 or greater treatment-related adverse events occurred in 84.1% of patients (232/276) with trastuzumab rezetecan and 67.9% (184/271) with chemotherapy, most commonly decreased neutrophil count (180 [65.2%] vs 147 [54.2%]). Conclusions and Relevance Trastuzumab rezetecan provided significant progression-free survival benefit over physician’s choice of chemotherapy in patients with ERBB2-low advanced breast cancer, with benefit observed across all key subgroups. It exhibited the potential as a new treatment option with a distinct safety profile in this setting. Trial Registration ClinicalTrials.gov Identifier: NCT05814354