Phase III, Randomized, Double-Blind Study Comparing the Efficacy, Safety, and Immunogenicity of SB3 (Trastuzumab Biosimilar) and Reference Trastuzumab in Patients Treated With Neoadjuvant Therapy for Human Epidermal Growth Factor Receptor 2-Positive Early Breast Cancer.

Purpose This phase III study compared SB3, a trastuzumab (TRZ) biosimilar, with reference TRZ in patients with human epidermal growth factor receptor 2-positive early breast cancer in the neoadjuvant setting ( ClinicalTrials.gov identifier: NCT02149524). Patients and Methods Patients were randomly assigned to receive neoadjuvant SB3 or TRZ for eight cycles concurrently with chemotherapy (four cycles of docetaxel followed by four cycles of fluorouracil, epirubicin, and cyclophosphamide) followed by surgery, and then 10 cycles of adjuvant SB3 or TRZ. The primary objective was comparison of breast pathologic complete response (bpCR) rate in the per-protocol set; equivalence was declared if the 95% CI of the ratio was within 0.785 to 1.546 or the 95% CI of the difference was within ± 13%. Secondary end points included comparisons of total pathologic complete response rate, overall response rate, event-free survival, overall survival, safety, pharmacokinetics, and immunogenicity. Results Eight hundred patients were included in the per-protocol set (SB3, n = 402; TRZ, n = 398). The bpCR rates were 51.7% and 42.0% with SB3 and TRZ, respectively. The adjusted ratio of bpCR was 1.259 (95% CI, 1.085 to 1.460), which was within the predefined equivalence margins. The adjusted difference was 10.70% (95% CI, 4.13% to 17.26%), with the lower limit contained within and the upper limit outside the equivalence margin. The total pathologic complete response rates were 45.8% and 35.8% and the overall response rates were 96.3% and 91.2% with SB3 and TRZ, respectively. Overall, 96.6% and 95.2% of patients experienced one or more adverse event, 10.5% and 10.7% had a serious adverse event, and 0.7% and 0.0% had antidrug antibodies (up to cycle 9) with SB3 and TRZ, respectively. Conclusion Equivalence for efficacy was demonstrated between SB3 and TRZ on the basis of the ratio of bpCR rates. Safety and immunogenicity were comparable.