154P Five-year follow-up of the phase III study comparing SB3 (trastuzumab biosimilar) and reference trastuzumab in patients with HER2 positive early or locally advanced breast cancer

Abstract

In the phase 3 study, SB3 (trastuzumab biosimilar) demonstrated similar efficacy, safety, PK, and immunogenicity to reference trastuzumab (TRZ) in patients with HER2 positive early or locally advanced breast cancer. Comparable cardiac safety profiles, and efficacy were observed between SB3 and TRZ at 4 years after randomisation in the phase 3 study. Here, we report the final follow-up results of the phase 3 study at 5 years. Patients were randomly assigned to receive 8 cycles of either SB3, or TRZ with concurrent neoadjuvant chemotherapy (4 cycles of docetaxel followed by 4 cycles of 5-fluorouracil/epirubicin/cyclophosphamide). Patients then underwent surgery followed by 10 cycles of SB3 or TRZ according to the previous treatment allocation to complete 1 year of treatment. After completing the adjuvant treatment, patients from selected countries were asked for consent to enroll in a follow-up observation study. The objective of the study was to monitor cardiac toxicity, event-free survival (EFS), and overall survival (OS). Of 875 patients randomised in the phase 3 study, 367 patients (SB3, N=186; TRZ, N=181) were enrolled in the follow-up study. The median follow-up duration was 68 months from randomisation. During the follow-up period, asymptomatic significant left ventricular ejection fraction (LVEF) decrease rarely occurred (SB3, n=1; TRZ, n=2). All three patients eventually recovered with LVEF ≥ 50%. Symptomatic congestive heart failure, or cardiac death was not reported. Events (recurrence, progression, or death) occurred in 32 patients (17.2%) in SB3 group, and 38 patients (21.0%) in TRZ group. 14 deaths (7.5%) and 23 deaths (12.7%) were reported in SB3 and TRZ groups, respectively. Hazard ratios (SB3/TRZ) for EFS, and OS were 0.78; 95% CI 0.48-1.25; p=0.30, and 0.62; 95% CI 0.32-1.22; p=0.17, respectively. 5-year EFS rates were 82.8% for SB3, and 79.7% for TRZ. 5-year OS rates were 93.1% for SB3, and 86.7% for TRZ. This five-year analysis of the subpopulation from the phase 3 study further supports similarity of SB3 and TRZ with comparable cardiac safety profile, and long-term efficacy. NCT02771795. Samsung Bioepis. Samsung Bioepis. F. Bazan: Financial Interests, Personal, Invited Speaker: Novartis; Financial Interests, Personal, Invited Speaker: Roche; Financial Interests, Personal, Invited Speaker: AstraZeneca; Financial Interests, Personal, Invited Speaker: Pfizer; Financial Interests, Personal, Invited Speaker: Clovis. H. Jang, S. Kim, J. Lee, Y.C. Yoon: Financial Interests, Personal, Full or part-time Employment: Samsung Bioepis. All other authors have declared no conflicts of interest.