Trastuzumab emtansine plus pertuzumab in Japanese patients with HER2-positive metastatic breast cancer: a phase Ib study.

Purpose: To investigate the safety, pharmacokinetics, and efficacy of trastuzumab emtansine (T-DM1) in combination with pertuzumab in Japanese patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer.
Patients and Methods: Patients with HER2-positive advanced or recurrent breast cancer who had received trastuzumab and chemotherapy-containing therapies were eligible. Patients received T-DM1 (3.6 mg/kg) with full-dose pertuzumab (a loading dose of 840 mg and then 420 mg) intravenously every 3 weeks. This study was registered at the Japan Pharmaceutical Information Center-Clinical Trials Information (JapicCTI-101234).
Results: Six patients enrolled in this study. The median duration of treatment was 11 (range 1-32) cycles. The most common treatment-emergent adverse event (TEAE) for any grade was diarrhea. Grade 3 or greater TEAEs included aspartate aminotransferase increased, left ventricular ejection fraction (LVEF) decreased, and neutrophil count decreased. The dose-limiting toxicity of grade 3 LVEF decreased was observed in one patient during cycle 1; however, it resolved within 30 days. The pharmacokinetic parameters of T-DM1 and pertuzumab were not affected by co-administration of the drugs. The best overall response included a partial response (PR) in 3 patients (50%) and stable disease (SD) in 2 patients (33%).
Conclusions: The combination of T-DM1 and pertuzumab was tolerated and showed exploratory efficacy in Japanese patients with HER2-positive metastatic breast cancer.