Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. ("Kelun-Biotech" or "the Company", 6990.HK) announced that results from the phase III registrational study of its novel human epidermal growth factor receptor 2 (HER2)-targeted antibody–drug conjugate (ADC) trastuzumab botidotin (舒泰莱^®) in HER2-positive unresectable or metastatic breast cancer (BC) have been published in Journal of Clinical Oncology (JCO, impact factor (IF)=44.7). Professor Xichun Hu and Professor Hongxia Wang of Fudan University Shanghai Cancer Center, and Dr. Junyou Ge, Director of the National Engineering Research Center of Targeted Biologics act as the co-senior authors. Professor Jian Zhang of Fudan University Shanghai Cancer Center, Professor Quchang Ouyang of Hunan Cancer Hospital, Professor Qingyuan Zhang of Harbin Medical University Cancer Hospital, Professor Huihui Li of Cancer Hospital of Shandong First Medical University, and Professor Xu Wang of Tianjin Medical University Cancer Institute and Hospital act as the co-first authors. These findings had previously been selected as a Late-Breaking Abstract (LBA) and presented as an oral presentation at the 2025 European Society for Medical Oncology (ESMO) Congress.

This randomized, open-label, multicenter phase III study was designed to evaluate the efficacy and safety of trastuzumab botidotin monotherapy versus trastuzumab emtansine (T-DM1) in patients with HER2-positive unresectable or metastatic BC who had received prior trastuzumab and taxane-containing regimens. A total of 365 patients were randomized 1:1 to receive trastuzumab botidotin or T-DM1. The primary endpoint was progression-free survival (PFS) assessed by blinded independent central review (BICR), and secondary endpoints included overall survival (OS), objective response rate (ORR), and duration of response (DoR).

As of the data cutoff date of April 26, 2025, with a median follow-up of 14.9 months, efficacy results showed:

• Median PFS was significantly prolonged in the trastuzumab botidotin group compared with the T-DM1 group (11.1 months vs. 4.4 months; hazard ratio (HR) = 0.39) (Figure A), meeting the primary endpoint of the study; consistent PFS benefit was observed across all prespecified subgroups (Figure B).
   
•  Trastuzumab botidotin group demonstrated deeper and more durable tumor responses compared with T-DM1 group, with an ORR of 76.9% vs. 53.0% and a median DoR of 12.2 months vs. 5.7 months (Figure C).
  
  
•  OS data were not mature in both groups, but an OS benefit trend was observed in trastuzumab botidotin group, demonstrating a 38% reduction in the risk of death (Figure D).

In terms of safety, patients in the trastuzumab botidotin group had a low incidence of interstitial lung disease (ILD), and the incidences of hematologic, hepatic, and gastrointestinal toxicities were notably lower than those in the T-DM1 group, along with lower rates of serious adverse events (SAEs) and treatment discontinuations. The most common treatment-related adverse events (TRAEs) in trastuzumab botidotin group were ocular events, which could be recovered or reversed after management with standardized strategies.

The publication of the phase III results for trastuzumab botidotin in Journal of Clinical Oncology marks a major international academic breakthrough for a domestically developed HER2 ADC backed by high-level clinical evidence. This is the first phase III trial in China for a HER2 ADC compared head-to-head with T-DM1 with positive results. The data showed that trastuzumab botidotin demonstrated improvements in key efficacy endpoints including PFS, ORR, and DoR, along with a favorable safety profile. Based on these positive results, trastuzumab botidotin has been approved by China's National Medical Products Administration (NMPA) for the treatment of second-line or later HER2-positive BC, becoming the first domestically developed HER2 ADC approved for this indication in China and providing a new treatment option for patients with HER2-positive advanced breast cancer.