Efficacy and safety of dasatinib with trastuzumab and paclitaxel in first line HER2-positive metastatic breast cancer: results from the phase II GEICAM/2010-04 study.

Background: An important proportion of HER2-positive metastatic breast cancer patients do not respond to trastuzumab. The combination of dasatinib and trastuzumab has shown to be synergistic in preclinical models.

Methods: We conducted a phase II trial combining dasatinib 100 mg once daily with trastuzumab 2 mg/kg and paclitaxel 80 mg/m weekly. Primary objective was objective response rate (ORR) and secondary included safety, other efficacy parameters and pharmacodynamics in tumour tissue, blood samples and skin biopsies.

Results: From June 2013 to December 2015, 29 patients were included. Median number of cycles was 12 (1-49). Only 6 patients discontinued due to adverse events. ORR was 79.3% (95% CI 60.3-92), clinical benefit rate 82.8% (95% CI 64.2-94.2). Median time to progression 23.9 months (95% CI 14.9-not reached [NR]), median progression-free survival 23.9 months (95% CI 10.3-NR). No grade 4 toxicity was seen. Grade 3 toxicities included: ejection fraction decrease, neutropenia, hyponatremia, fatigue and sensory neuropathy and one left ventricular systolic dysfunction. Phosphorylated (p)-SRC was reduced in peripheral blood mononuclear cells. Phosphorylated SRC, ERK and AKT were also reduced in epidermal keratinocytes.

Conclusions: Dasatinib can be safely combined with trastuzumab and paclitaxel. The combination is active with an ORR of almost 80%.

Trial Registration: NCT01306942, EudraCT 2010-023304-27.