Against a comparator producing 4.4 months of median progression-free survival, trastuzumab botidotin delivered 11.1 months in a head-to-head Phase 3 trial, a hazard ratio of 0.39 that halved the expected benchmark for this treatment line. Those results, now published in the Journal of Clinical Oncology, give Kelun-Biotech’s HER2-targeted ADC its fullest public data package since the NMPA approved it in October 2025 for adults with unresectable or metastatic HER2-positive breast cancer who had received at least one prior anti-HER2 therapy.
The 365-patient randomized study compared trastuzumab botidotin monotherapy against T-DM1 in patients who had already received trastuzumab and taxane-based regimens, the population where second-line options carry the most weight. The response data reinforce the PFS finding: 76.9% of patients on trastuzumab botidotin responded versus 53.0% on T-DM1, and those responses lasted a median of 12.2 months compared to 5.7 months. Overall survival data were immature at the April 2025 cutoff, though a 38% reduction in the risk of death was observed in the trastuzumab botidotin arm, a trend the authors will need longer follow-up to confirm.
The safety read matters as much as the efficacy numbers here, because the known liability of HER2 ADCs is interstitial lung disease. Trastuzumab botidotin showed low ILD incidence, and rates of hematologic, hepatic, and gastrointestinal toxicities ran below T-DM1 levels. The dominant treatment-related adverse event was ocular toxicity, a class effect tied to the drug’s MMAF-derivative payload; the investigators report it was manageable and reversible with standardized protocols. Serious adverse event rates and treatment discontinuations were lower in the trastuzumab botidotin arm, which matters practically for patients staying on therapy long enough to realize the PFS benefit.
The JCO publication follows the data’s debut as a late-breaking oral presentation at ESMO 2025, and it arrives as the HER2 ADC field has grown increasingly crowded globally. Kelun-Biotech has also opened a Phase 2 study of trastuzumab botidotin in patients who previously received a topoisomerase inhibitor payload ADC, the next sequencing question that will determine whether this drug has utility beyond its current approved line. The durability of the 12.2-month median response in that pretreated population will be the number to watch.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
