Trastuzumab Biosimilar Offers Equivalent Efficacy in HER2-Positive Breast Cancer

A trastuzumab biosimilar known as SB3 showed equivalent efficacy and safety to trastuzumab itself in a phase III trial of women with early HER2-positive breast cancer in the neoadjuvant setting.

“Biotherapies are expensive and not readily available in some countries,” wrote study authors led by Xavier Pivot, MD, PhD, of the Institut Régional du Cancer in Strasbourg, France. “As a result, economical biosimilars may increase patient access to critical therapies in some areas and save costs, thereby facilitating the availability of resources for innovative biotherapies in other countries.”

The new phase III trial included 800 patients randomized to either trastuzumab (398 patients) or SB3 (402 patients); all patients had early HER2-positive breast cancer, and were treated with the study drug concurrently with chemotherapy followed by surgery and then 10 cycles of adjuvant SB3 or trastuzumab. The results were published online ahead of print in the Journal of Clinical Oncology.

The median age in the study was 51 years, and most patients (52.8%) had T2 disease and clinically involved lymph nodes (79.5%). In a per-protocol analysis, the SB3 group achieved a breast pathologic complete response of 51.7%, compared with 42% in the trastuzumab group; this yielded an adjusted ratio of 1.259, which was within the study’s equivalence margins. In a full analysis set, those rates were 49% and 39.7%, respectively, and the adjusted ratio was 1.243.

The total pathologic complete response rates were 45.8% with SB3 and 35.8% with trastuzumab, and this was similar in the full analysis set.

Most patients in both groups experienced at least one treatment-emergent adverse event (TEAE), at 96.6% of the SB3 patients and 95.2% of the trastuzumab patients. The most common TEAEs included neutropenia, alopecia, nausea, and leucopenia. There were four TEAEs resulting in death (one in the SB3 group, three in the trastuzumab group), though none of these were deemed related to the study drug. The two groups had a similar incidence of TEAEs considered to be of “special interest.”

“This study demonstrated similarity between SB3 and trastuzumab,” the authors concluded. “A comprehensive evaluation of the full data, including similarity in clinical efficacy, safety, pharmacokinetics, and immunogenicity of the proposed biosimilar and the reference drug, is recommended.”