Efficacy, Safety, and Immunogenicity of HLX02 Compared with Reference Trastuzumab in Patients with Recurrent or Metastatic HER2-Positive Breast Cancer: A Randomized Phase III Equivalence Trial

Background HLX02 is an approved biosimilar of trastuzumab. Objective This study aimed to evaluated the efficacy, safety, and immunogenicity of HLX02 compared with reference trastuzumab in patients with human epidermal growth factor receptor 2 (HER2)-positive recurrent or metastatic breast cancer. Patients and Methods This randomized, double-blind, phase III study was conducted at 89 centers in China, the Philippines, Poland, and Ukraine. Eligible patients were randomized (1:1) to receive HLX02 or European Union (EU)-sourced trastuzumab (initial dose of 8 mg/kg, followed by 6 mg/kg every 3 weeks for up to 12 months) in combination with docetaxel intravenously. The primary endpoint was overall response rate up to week 24 (ORR24). Equivalence was declared if the 95% confidence interval (CI) of difference was within +/- 13.5%. Safety and immunogenicity were evaluated in patients who received at least one dose of study medication. Results Between 11 November 2016 and 10 July 2019, a total of 649 patients were enrolled. The ORR24 was 71.3 and 71.4% in the HLX02 (n = 324) and EU-trastuzumab (n = 325) groups, with a difference of - 0.1% (95% CI - 7 to 6.9), which fell entirely in the predefined equivalence margins. No statistically significant differences were observed in all secondary efficacy analyses. Safety profiles and immunogenicity were comparable in HLX02 and EU-trastuzumab groups. In total, 98.8% of patients in each group experienced at least one treatment-emergent adverse event (TEAE), 23.8 and 24.9% experienced serious TEAEs, and 0.6% in each group had antidrug antibodies. Conclusions Among patients with HER2-positive recurrent or metastatic breast cancer, HLX02 demonstrated equivalent efficacy and similar safety and immunogenicity to reference trastuzumab. Plain Language Summary Trastuzumab is a biologic drug used to treat patients with certain types of breast cancer and stomach cancer. Biosimilars are medications that are almost identical to and indistinguishable from original biologic drugs but usually less expensive and more accessible. The main purpose of this study was to evaluate the efficacy (treatment effects) of HLX02 (trastuzumab biosimilar) compared with reference trastuzumab in patients with human epidermal growth factor receptor 2 (HER2)-positive recurrent or metastatic breast cancer. Other objectives were to evaluate the safety of HLX02 by monitoring adverse events and assessing its potential to induce antibody production (which can prevent a drug from being effective). Patients with HER2-positive recurrent or metastatic breast cancer were randomly allocated to receive HLX02 (n = 324) or European Union (EU)-sourced trastuzumab (n = 325). Study drugs (HLX02 or EU-trastuzumab) were given intravenously, with an initial dose of 8 mg/kg, followed by 6 mg/kg every 3 weeks for up to 12 months. Statistical analyses showed that HLX02 was equivalent to trastuzumab in efficacy evaluations. Adverse events observed in the HLX02 treatment group were consistent with those seen with trastuzumab in the current and previous clinical studies. Additionally, no statistically significant differences were seen in the tendency to stimulate antibody production between the two study drugs. To conclude, HLX02 and reference trastuzumab had similar efficacy and safety profiles. These data support the approval of HLX02 as a trastuzumab biosimilar.