BACKGROUND: This randomised, double-blind study compared PF-05280014 (a trastuzumab biosimilar) with reference trastuzumab (Herceptin) sourced from the European Union (trastuzumab-EU), when each was given with paclitaxel as first-line treatment for HER2-positive metastatic breast cancer.METHODS: Between 4 April 2014 and 22 January 2016, 707 participants were randomised 1:1 to receive intravenous PF-05280014 plus paclitaxel (PF-05280014 group; n=352) or trastuzumab-EU plus paclitaxel (trastuzumab-EU group; n=355). PF-05280014 or trastuzumab-EU was administered weekly (first dose 4mg/kg, subsequent doses 2mg/kg), with the option to change to a 3-weekly regimen (6mg/kg) from Week 33. Treatment with PF-05280014 or trastuzumab-EU could continue until disease progression. Paclitaxel (starting dose 80mg/m2) was administered on Days 1, 8 and 15 of 28-day cycles for at least six cycles or until maximal benefit of response. The primary endpoint was objective response rate (ORR), evaluating responses achieved by Week 25 and confirmed by Week 33, based on blinded central radiology review.RESULTS: The risk ratio for ORR was 0.940 (95% CI: 0.842-1.049). The 95% CI fell within the pre-specified equivalence margin of 0.80-1.25. ORR was 62.5% (95% CI: 57.2-67.6%) in the PF-05280014 group and 66.5% (95% CI: 61.3-71.4%) in the trastuzumab-EU group. As of data cut-off on 11 January 2017 (using data up to 378 days post-randomisation), there were no notable differences between groups in progression-free survival (median: 12.16 months in the PF-05280014 group vs. 12.06 months in the trastuzumab-EU group; 1-year rate: 54% vs. 51%) or overall survival (median: not reached in either group; 1-year rate: 89.31% vs. 87.36%). Safety outcomes and immunogenicity were similar between the treatment groups.CONCLUSION: When given as first-line treatment for HER2-positive metastatic breast cancer, PF-05280014 plus paclitaxel demonstrated equivalence to trastuzumab-EU plus paclitaxel in terms of ORR.CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, NCT01989676.
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