The 5-year follow-up results of a comparative phase 3 study further support the similarity of SB3 and trastuzumab reference with respect to cardiac safety profile and long-term efficacy.
A randomized phase 3 study demonstrated the bioequivalence of the trastuzumab reference to its biosimilar SB3 in terms of efficacy, safety, pharmacokinetics, and immunogenicity in patients with HER2-positive early or locally advanced breast cancer. In a subset of patients from a phase 3 study, a follow-up observation study was conducted for an additional 5 years to assess cardiac safety and survival outcomes, the results of which were reported at the 2021 European Society for Medical Oncology Annual Meeting.
Eligible patients were randomized to receive SB3 or trastuzumab reference for 8 cycles, with concurrent neoadjuvant chemotherapy consisting of 4 cycles of docetaxel followed by 4 cycles of 5-fluorouracil/epirubicin/cyclophosphamide. Following surgery, 10 cycles of SB3 or trastuzumab reference were continued for 1 year of treatment.
Of the total 875 patients who were randomized in the phase 3 study, a subset of 367 patients were enrolled in the follow-up study. From randomization, the median follow-up duration was 68 months. During the follow-up period, the incidence of asymptomatic significant left ventricular ejection fraction decrease was rare, with 1 event reported in the SB3 group and 2 in the trastuzumab reference group. These events were reported within 2 years of first administration of the drugs and all patients recovered, with left ventricular ejection fraction >50%. There were no reports of symptomatic congestive heart failure or cardiac death.
Survival analysis after 32 patients (17.2%) in the SB3 group and 38 patients (21.0%) in the trastuzumab reference group experienced events (recurrence, progression, or death) resulted in similar hazard ratios (SB3/trastuzumab reference) for event-free survival (0.78; 95% confidence interval, 0.48-1.25; P = .30), and overall survival (0.62; 95% confidence interval, 0.32-1.22; P = .17). The 5-year event-free survival (82.8% vs 79.7%) and 5-year overall survival rates were also similar between the groups (93.1% vs 86.7%).
The results of this 5-year follow-up study further support the similarity of SB3 and trastuzumab reference with respect to cardiac safety profile and long-term efficacy.
Source: Pivot X, Burian O, Bazan F, et al. 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. Ann Oncol. 2021;32(suppl_5):S428.