Abstract PO1-29-03: Efficacy, Safety, and Immunogenicity of TQ-B211 (a Trastuzumab Biosimilar) Plus Docetaxel versus Herceptin® Plus Docetaxel for HER2-positive Metastatic Breast Cancer: a Double-blind, Randomised, Multicenter, Phase 3 Trial

Abstract Background: Breast cancer is one of the most common malignant tumors in women worldwide. In China, the incidence of breast cancer has been steadily increasing. Approximately 30% of human breast cancers exhibit human epidermal growth factor receptor 2 (HER2) positivity, which is closely associated with tumor aggressiveness, high recurrence rate and high mortality. This study aimed to evaluate the efficacy, safety, and immunogenicity of TQ-B211 (a trastuzumab biosimilar) compared to the reference trastuzumab in combination with docetaxel as first-line treatment for patients with HER2-positive metastatic breast cancer. Methods: This randomized, multicenter, double-blind phase III equivalence study enrolled HER2+ metastatic breast cancer patients aged 18-75, ECOG PS ≤1, no prior systemic chemotherapy, biologic, or targeted therapy for recurrent or metastatic disease, and at least one measurable lesion (RECIST 1.1). The patients were randomly assigned to two groups: the experimental group received TQ-B211 (8 mg/kg iv on day 1, cycle 1, followed by 6 mg/kg q3w for cycles 2-8) in combination with docetaxel (75 mg/m2 on day 2, cycle1, followed by 75 mg/m2 on day 1 for cycles 2-8), while the control group received Herceptin® in combination with docetaxel. For subjects who completed 8 cycles of treatment without disease progression and demonstrated tolerability, they were subsequently administered TQ-B211 as monotherapy until disease progression or unsuitable for further treatment. The primary efficacy endpoint was ORR up to week 24 (ORR24w). Equivalence was declared if the 90% confidence interval (CI) of relative ratio (RR) value was within the range of 0.8 to 1.25. Secondary efficacy endpoints included duration of response (DoR); progression-free survival (PFS); disease control rate (DCR); overall survival (OS), safety and immunogenicity. Results: Between December 6, 2018 and July 31, 2021, a total of 386 patients (pts) were enrolled (192 pts in the TQ-B211 group and 194 pts in the Herceptin® group). In the intention-to-treat (ITT) population, the ORR24w of the TQ-B211 group was 67.19% (95% CI: 60.55, 73.83), while the ORR24w of the Herceptin® group was 65.98% (95% CI: 59.31, 72.65). The RR of the confirmed ORR24w between the two groups was 1.02 (90%CI, 0.90, 1.15), which fell entirely in the predefined equivalence margins (0.8, 1.25), indicating comparable efficacy of the two drugs. In the ITT population, the DCR of the TQ-B211 group and the Herceptin® group were 83.85% (78.65, 89.06) and 78.35% (72.56, 84.15) respectively, with no statistically significant difference between the two groups (P=0.1940). By the data cutoff date of October 31, 2021, the median PFS was not statistically different (P=0.6834); the median OS was not reached in both groups (P=0.9246). Additionally, the data results of the per-protocol (PP) population were similar to those of the ITT population. In total, similar rates of treatment-related grade ≥3 adverse events (41.05% vs. 46.39%) occurred in the TQ-B211 and Herceptin® groups, respectively. The incidence and magnitude of immunogenicity were low in both of the two groups (ADA: 0.53% vs. 0%, Nab: both negative). Conclusion: Equivalence for efficacy was demonstrated between TQ-B211 and Herceptin® on the basis of ORR24w. Safety and immunogenicity were comparable. Citation Format: Xichun Hu, Qingyuan Zhang, Shusen Wang, Tao Sun, Xiaohua Zeng, Weimin Xie, Zhongsheng Tong, Hui Cao, Huihua Xiong, Xiuwen Wang, Jin Yang, Shuqun Zhang, Ying Wang, Chunhong Hu, Kaijian Lei, Binlin Ma, Wei Liu, Zhiyong Yu, PeiJian Peng, Hongwei Yang, Zhijun Yuan, Xiaojia Wang, Xujuan Wang, Hong Wang, Yongqian Shu, Nanlin Li, Wenbin Yue, Jingfen Wang, Daqing Wang, Zhiguo Luo, Junyang Mo, Yarong Li, Lili Sheng. Efficacy, Safety, and Immunogenicity of TQ-B211 (a Trastuzumab Biosimilar) Plus Docetaxel versus Herceptin® Plus Docetaxel for HER2-positive Metastatic Breast Cancer: a Double-blind, Randomised, Multicenter, Phase 3 Trial abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-29-03.