Introduction: The present study for biosimilar trastuzumab was a multicentric, randomized, two-arm parallel-group, comparative phase III study in patients with metastatic breast cancer.
Materials and methods: Stage I of the study was conducted among 42 participants with equal distribution in the study and reference arm. After a loading dose of 8 mg/kg trastuzumab was administered intravenously on day 1 of the first cycle; serum samples were obtained at 0, 1.5 (end of IP infusion), 3, 6, 8, 24, 96, 168, and 336 h after the first infusion for the first cycle only. Cmax and AUC0-336 were calculated for a single dose. Stage II enrolled a total of 106 patients across 20 centers who were randomized to receive biosimilar trastuzumab (study trastuzumab) or the reference trastuzumab with paclitaxel. The primary endpoint of the objective response rate (ORR) was analyzed after last the dosed participant had completed 25-week evaluation. The secondary outcome measures included time to tumor progression, progression-free survival and overall survival at week 48, and safety evaluation.
Results: For reference and study trastuzumab products, mean Cmax of 229.02 and 210.68 μg/mL and AUC0-336 of 24298.29 and 25809.33 (μg × h/mL), respectively, were obtained. The efficacy results demonstrated that study trastuzumab and reference trastuzumab had comparable ORR (48.44% vs. 44.44%). The proportions of participants showing complete response and partial response in each arm were found to be comparable. There were 56 (68.29%) participants in the study arm and 13 (59.09%) participants in the reference arm who had at least one adverse event during the study. Immunogenicity assessment also revealed no participants with positive antibody titer in any of the study arms.
Conclusion: The pharmacokinetics, overall response rate at 25 weeks, and safety of the biosimilar trastuzumab was comparable to the reference trastuzumab.
Keywords: Breast cancer; complete response; human epidermal growth factor receptor 2+; objective response rate; partial response; pharmacokinetics; trastuzumab.