Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. said results from a phase III registrational study of its HER2-targeted antibody-drug conjugate trastuzumab botidotin in HER2-positive unresectable or metastatic breast cancer have been published in the Journal of Clinical Oncology. The company said the findings had previously been selected as a late-breaking abstract and presented as an oral presentation at the 2025 European Society for Medical Oncology Congress.
The company said the randomized, open-label, multicenter phase III study compared trastuzumab botidotin monotherapy with trastuzumab emtansine (T-DM1) in patients who had received prior trastuzumab and taxane-containing regimens. A total of 365 patients were randomized 1:1, with progression-free survival assessed by blinded independent central review as the primary endpoint and overall survival, objective response rate and duration of response as secondary endpoints. The data cutoff was April 26, 2025, with a median follow-up of 14.9 months.
On safety, the company said patients in the trastuzumab botidotin group had a low incidence of interstitial lung disease, and that rates of hematologic, hepatic and gastrointestinal toxicities were notably lower than in the T-DM1 group, along with lower rates of serious adverse events and treatment discontinuations. The most common treatment-related adverse events in the trastuzumab botidotin group were ocular events, which the company said could be recovered or reversed after management with standardized strategies.
The company said the data showed improvements in progression-free survival, objective response rate and duration of response, with a favorable safety profile. It said trastuzumab botidotin has been approved by China's National Medical Products Administration for second-line or later HER2-positive breast cancer, describing it as the first domestically developed HER2 ADC approved for that indication in China. According to the company, the approval was based on the phase 3 KL166-III-06 study, where a pre-specified interim analysis showed a statistically significant and clinically meaningful improvement in progression-free survival by blinded independent central review compared with T-DM1, with a beneficial trend for overall survival also observed. A phase 2 study has been initiated in patients with HER2-positive unresectable or metastatic breast cancer who previously received a topoisomerase inhibitor payload ADC, the company said.