HORIZON-Breast01 at a Glance
Design: multicentre (50 China sites), open-label, randomised (1:1) phase 3; N=287 (all female, median age 55). PFS (primary, BICR): 30.6 vs 8.3 mo; HR 0.22 (0.15-0.34), p<0.0001. 12-mo PFS: 84.7% vs 35.5%. ORR: 81.7% vs 55.9%. Comparator: pyrotinib + capecitabine (NOT T-DXd). Regulatory: investigational. Source: Lancet Oncol 2026 (PubMed 42385760); data cutoff Jun 30, 2025; first presented ESMO 2025 (LBA19).
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Trastuzumab rezetecan versus a TKI-based standard of care
Trastuzumab rezetecan (SHR-A1811) is a HER2-directed antibody-drug conjugate. HORIZON-Breast01 evaluated it against pyrotinib plus capecitabine — an established standard of care in this setting — in patients with HER2-positive unresectable or metastatic breast cancer whose disease had progressed following trastuzumab and a taxane. An important interpretive consideration is that the comparator is a pan-HER tyrosine kinase inhibitor regimen (pyrotinib + capecitabine), not trastuzumab deruxtecan (T-DXd); the trial therefore establishes efficacy relative to a TKI-based standard rather than in direct comparison with another antibody-drug conjugate. The agent remains investigational and is not FDA approved.
Progression-Free Survival (primary endpoint)
Statistically significant progression-free survival benefit
Median progression-free survival was 30.6 months (95% CI 16.8–NR) with trastuzumab rezetecan versus 8.3 months (6.9–11.0) with pyrotinib plus capecitabine (HR 0.22; 95% CI 0.15–0.34; p<0.0001). The 12-month progression-free survival rate was 84.7% versus 35.5%, and the confirmed objective response rate was 81.7% versus 55.9%. The treatment effect was consistent across prespecified subgroups (HER2 IHC 3+ HR 0.24; hormone-receptor-positive HR 0.23; visceral metastases HR 0.24). Overall survival data were immature at this interim analysis, with a trend favouring trastuzumab rezetecan. Source: Lancet Oncol 2026 (PubMed 42385760); interim analysis, data cutoff 30 June 2025; PFS by blinded independent central review. PubMed
HR 0.22 — a 78% relative reduction in the risk of progression or deathSafety and Tolerability
Grade ≥3 haematologic adverse events
Grade ≥3 treatment-related adverse events with trastuzumab rezetecan were predominantly haematologic: decreased neutrophil count 54% versus 9%, decreased white blood cell count 20% versus 3%, and decreased platelet count 11% versus 1%. Treatment-related serious adverse events occurred in 13% versus 12%. Interstitial lung disease was reported in 3% (4/142). Two adverse events led to death (one case of septic shock unrelated to trastuzumab rezetecan, and one event related to the control regimen). All safety figures on this page are drawn from the primary publication. Source: Lancet Oncol 2026 (PubMed 42385760).
Key Figures (with OCR)
Oncologist commentary from the KOL Pulse network
HORIZON-Breast01 - FAQ
What is HORIZON-Breast01?
A phase 3 randomised trial (NCT05424835) of trastuzumab rezetecan (SHR-A1811, a HER2 ADC) vs pyrotinib + capecitabine in HER2-positive metastatic breast cancer after trastuzumab and a taxane.
What was the primary result?
Median PFS 30.6 vs 8.3 months (HR 0.22, 95% CI 0.15-0.34, p<0.0001); 12-month PFS 84.7% vs 35.5%.
How does the safety compare?
Grade ≥3 treatment-related AEs with the ADC included decreased neutrophils (54% vs 9%), WBC (20% vs 3%), and platelets (11% vs 1%); ILD 3%.
Is it FDA approved?
No - investigational. The interim analysis was published in The Lancet Oncology (Jul 1, 2026); sponsor Jiangsu Hengrui Pharmaceuticals (Glenmark licensed ex-China).
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