SHR-A1201 is an antibody-drug conjugate (ADC) that combines trastuzumab with DM1 (a chemotherapeutic agent) using a chemical connector. This phase I study investigated the safety, tolerability and pharmacokinetics of SHR-A1201 in patients with human epidermal growth factor receptor 2-positive advanced breast cancer. This phase I study enrolled patients in a traditional 3 + 3 dose-escalation design to receive a single dose of SHR-A1201 (1.2 mg/kg, 2.4 mg/kg, 3.6 mg/kg or 4.8 mg/kg). The observation period of dose-limiting toxicity (DLT) was 21 days. A total of 12 patients were enrolled and received SHR-A1201. Most treatment-emergent adverse events (TEAEs) were grade 1 or 2 in severity, with elevated aspartate aminotransferase (75%), thrombocytopenia (75%), and nausea (66.7%) being reported most frequently. The common grade 3 TEAEs were thrombocytopenia and decreased lymphocyte count, and there were no grade 4 or above TEAEs. There were no serious adverse events or drug-related deaths. One DLT occurred in one patient treated with SHR-A1201 4.8 mg/kg (asymptomatic grade 3 increased γ-glutamyltransferase). The maximum tolerated dose of SHR-A1201 was not lower than that of T-DM1 (3.6 mg/kg). A total of 8.3% (1/12) of patients had ADA-positive reactions 504 h after administration, but no differences were observed in the type, incidence, or severity of TEAEs between patients with and without ADA. SHR-A1201 exhibited the pharmacokinetics characteristics of typical ADCs. An encouraging antitumor effect was observed in the 4.8 mg/kg dose group. SHR-A1201 was well tolerated and safe in patients with advanced HER2-positive breast cancer. The pharmacokinetics parameters showed a linear trend, and the immunogenicity results met the clinical expectations.
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