SB3, a biosimilar to trastuzumab, shows similar clinical efficacy, without increased toxicity, to its reference product for the treatment of HER2-positive breast cancer, according to a study published in the Journal of Clinical Oncology.1

Previous studies suggest that SB3 has similar pharmacokinetic activity to trastuzumab. For this randomized phase 3 study ( Identifier: NCT02149524), researchers evaluated whether neoadjuvant SB3 shows an equivalent pathologic complete response rate in primary breast tumors to trastuzumab among patients with HER2-positive disease.

Of 1254 patients screened for treatment, 875 were randomly assigned to receive SB3 (437 patients) or trastuzumab (438 patients). Patients received SB3 or trastuzumab, both with chemotherapy, before surgery; patients were stratified by hormone receptor status. The median age was 51 years, 52.8% had stage T2 disease, and 40.9% of patients were hormone receptor–negative. Baseline characteristics were well-balanced.

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Four hundred and two patients in the SB3 group and 398 in the trastuzumab group underwent neoadjuvant therapy and surgery. The median follow-up was 337 days in the SB3 group and 338 days in the trastuzumab group.

In the per-protocol set, the complete response rates in primary breast tumors were 51.7% and 42% in the SB3 and trastuzumab groups, respectively; the overall response rates were 96.3% and 91.2%, respectively.

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The rates of adverse events were similar, with 96.6% of patients in the SB3 group and 95.2% of patients in the trastuzumab group reporting at least 1 adverse event; 10.5% and 10.7% of patients, respectively, reported a serious adverse event.

The authors concluded that “this study demonstrated similarity between SB3 and [trastuzumab]. Patients may continue in a long-term extension study ( identifier: NCT02771795) that will further monitor safety, event-free survival, and overall survival.”


  1. Pivot X, Bondarenko I, Nowecki Z, et al. Phase III, randomized, double-blind study comparing the efficacy, safety, and immunogenicity of SB3 (trastuzumab biosimilar) and reference trastuzumab in patients treated with neoadjuvant therapy for human epidermal growth factor receptor 2–positive early. J Clin Oncol. 2018 Jan 26. doi: 10.1200/JCO.2017.74.0126 [Epub ahead of print]