Chinese biopharmaceutical company Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. (HKG: 6990) on Monday announced that it has published phase III results for its HER2-targeted antibody–drug conjugate trastuzumab botidotin in unresectable or metastatic HER2-positive breast cancer in Journal of Clinical Oncology.

The open-label, multicentre study compared trastuzumab botidotin monotherapy with trastuzumab emtansine (T-DM1) in 365 patients previously treated with trastuzumab and taxane-based regimens. Progression-free survival assessed by blinded independent central review was the primary endpoint, with overall survival, objective response rate and duration of response as secondary measures.

After a median follow-up of 14.9 months, median progression-free survival was 11.1 months for trastuzumab botidotin versus 4.4 months for T-DM1, corresponding to a hazard ratio of 0.39. Objective response rate was 76.9% compared with 53.0%, and median duration of response was 12.2 months versus 5.7 months.

Safety findings showed lower rates of interstitial lung disease, haematologic, hepatic and gastrointestinal toxicities in the trastuzumab botidotin group than the T-DM1 group, with fewer serious adverse events and treatment discontinuations.

Trastuzumab botidotin combines a HER2 monoclonal antibody with a monomethyl auristatin F derivative via a stable, enzyme-cleavable linker, delivering cytotoxic activity and antibody-dependent cell-mediated cytotoxicity. Following the KL166-III-06 phase III study, which met its primary endpoint at interim analysis, the drug has been approved for marketing by the National Medical Products Administration for second-line or later HER2-positive breast cancer.