Multicenter phase II trial of Genexol-PM, a Cremophor-free, polymeric micelle formulation of paclitaxel, in patients with metastatic breast cancer

Genexol-PM is a novel Cremophor EL-free polymeric micelle formulation of paclitaxel. This single arm, multicenter phase II study was designed to evaluate the efficacy and safety of Genexol-PM in patients with histologically confirmed metastatic breast cancer (MBC). Forty-one women received Genexol-PM by intravenous infusion at 300 mg/m² over 3 h every 3 weeks without premedication until disease progression or intolerability. A total of 331 chemotherapy cycles were administered, with a median of 8 cycles per patient (range, 1-16). Overall response rate was 58.5% (95% CI: 43.5-72.3) with 5 complete responses and 19 partial responses. Thirty-seven patients who received Genexol-PM as a first-line therapy for their metastatic disease showed a response rate of 59.5% (95% CI: 43.5-73.7), and two responses were reported in four patients treated in the second-line setting for their metastatic disease. The median time to progression (TTP) for all patients was 9.0 months (range, 1.0-17.0+ months). Grade 3 non-hematologic toxicities included sensory peripheral neuropathy (51.2%), and myalgia (2.4%). Eight patients (19.5%) experienced hypersensitivity reactions, with grade 3 in two patients. Hematologic toxicities were grade 3 and 4 neutropenia (51.2 and 17.1%, respectively), and grade 1 and 2 thrombocytopenia (22.0%). Notably, no febrile neutropenia was observed. Genexol-PM appears a promising new paclitaxel in view of significant efficacies. Further trials with different dosing schedules, durations of delivery, or in combination with other drugs are warranted.