Evaluation of Biosimilar Trastuzumab MYL-1401O in HER2-Positive Breast Cancer

OBJECTIVES: The trastuzumab biosimilar MYL-1401O has demonstrated equivalent efficacy and comparable safety to reference trastuzumab (RTZ) in clinical trials of human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC) as HER2 monotherapy.STUDY DESIGN: Here, we present the first real-world comparison of MYL-1401O vs RTZ as single/dual HER2-targeted therapy for the neoadjuvant, adjuvant, and palliative treatment of HER2-positive breast cancer in the first and second lines.METHODS: We retrospectively investigated medical records. We identified patients with HER2-positive early-stage breast cancer (EBC) (n = 159) who had received neoadjuvant chemotherapy with RTZ or MYL-1401O +/- pertuzumab (n = 92) or adjuvant chemotherapy with RTZ or MYL-1401O plus taxane (n = 67) between January 2018 and June 2021, as well as patients with MBC (n = 53) who had received palliative first-line treatment with RTZ or MYL-1401O and docetaxel +/- pertuzumab or second-line treatment with RTZ or MYL-1401O and taxane between January 2018 and June 2021.RESULTS: The rate of achieving pathologic complete response in patients receiving neoadjuvant chemotherapy was similar between those receiving MYL-1401O and RTZ (62.7% [37/59] and 55.9% [19/34], respectively; P = .509). Progression-free survival (PFS) at 12, 24, and 36 months was similar in the 2 cohorts of the EBC-adjuvant group: 96.3%, 84.7%, and 71.5%, respectively, in patients receiving MYL-1401O, and 100%, 88.5%, and 64.8% in patients receiving RTZ (P = .577). Median PFS was also similar in MBC, at 23.0 months (95% CI, 9.8-26.1) in patients receiving MYL-1401O and 23.0 months (95% CI, 19.9-26.0) in patients receiving RTZ (P = .270). The overall response rate, disease control rate, and cardiac safety profiles did not show significant differences in efficacy outcomes between the 2 groups. CONCLUSIONS: These data suggest that biosimilar trastuzumab MYL-1401O has similar effectiveness and cardiac safety to RTZ in patients with HER2-positive EBC or MBC.