Safety and Clinical Evaluation of Dual Inhibition with Pertuzumab and Trastuzumab Biosimilar SB3 in HER2-Positive Breast Cancer Patients.

Background: The addition of trastuzumab to standard chemotherapy has improved survival in patients with HER2-positive breast cancer in neoadjuvant, adjuvant, and metastatic settings. In higher tumor stages, the addition of pertuzumab is now a standard of care and associated with a favorable toxicity profile. We evaluated the safety and efficacy of the trastuzumab biosimilar SB3 in combination with pertuzumab in HER2-positive breast cancer patients.

Methods: Seventy-eight patients with HER2-positive breast cancer treated at the Division of Oncology at the Medical University of Graz were included. Summary measures are reported as medians (25th to 75th percentile) for continuous variables and as absolute frequencies (%) for count data.

Results: Thirty-five patients received a median of 4 (3-7) cycles of trastuzumab biosimilar SB3 plus pertuzumab. All patients had a normal baseline left ventricular ejection fraction (LVEF; >50%) prior to the initiation of SB3 plus pertuzumab treatment with a median LVEF of 60% (60-65). Twenty-one patients had a median absolute LVEF decline of 1% (-5 to 0). Two patients (5.7%) had a LVEF reduction ≤50%, but none ≥10%. There were no unexpected adverse events. Twenty-two of 35 patients (63%) were treated with trastuzumab biosimilar SB3 and pertuzumab in the neoadjuvant setting and 11 patients (50%) achieved a pathological complete response. The safety and the efficacy in this setting was comparable to the trastuzumab plus pertuzumab combination in neoadjuvantly treated matched samples.

Conclusion: In this series of HER2-positive breast cancer patients, the combination of SB3 plus pertuzumab was consistent with the known safety and efficacy profile of trastuzumab and pertuzumab combination.