SHR-A1811, a novel HER2-targeting antibody-drug conjugate, in advanced solid tumors (HORIZON-X): a global phase 1 trial

SHR-A1811, an antibody‒drug conjugate consisting of the anti-HER2 antibody trastuzumab conjugated via a cleavable linker to a topoisomerase I inhibitor payload, demonstrated substantial antitumor activity in patients with heavily treated HER2-expressing or mutated advanced solid tumors. The main analysis was reported, and this is a long-term follow-up of the HORIZON-X trial (NCT04446260). This global, multicenter, first-in-human, phase 1 trial enrolled patients aged ≥ 18 years with unresectable, advanced, or metastatic HER2-expressing or mutated solid tumors refractory or intolerant to standard therapies across 38 hospitals. SHR-A1811 was administered intravenously at doses ranging from 1.0 to 8.0 mg/kg every three weeks. The primary endpoints included dose-limiting toxicity, safety, and the recommended phase 2 dose. From September 7, 2020, to June 4, 2024, 396 patients with a median of three prior treatment regimens (IQR 2-5) received SHR-A1811. As of March 12, 2025, the median follow-up was 17.1 months for HER2-positive breast cancer, 10.6 months for HER2-low expressing breast cancer, and 4.3 to 8.2 months in non-breast cancers. The safety profile remained consistent with that of previous reports. Grade 3 or higher treatment-related adverse events occurred in 261 patients (65.9%), and any grade interstitial lung disease was observed in 10 patients (2.5%). The median progression-free survival was 25.0 months (95% CI 17.2-33.6) for HER2-positive breast cancer, 11.0 months (95% CI 8.2-13.8) for HER2-low expressing breast cancer, and 3.5 to 17.2 months for non-breast tumors. This final analysis further confirmed the long-term efficacy and favorable safety profile of SHR-A1811 among heavily prior-treated advanced solid tumors, reinforcing its potential as an effective HER2-targeted therapy.