Phase II trial of ixabepilone, an epothilone B analog, given daily for three days every three weeks, in metastatic breast cancer

Twelve patients with metastatic breast cancer previously exposed to taxanes were treated on a Phase II trial with ixabepilone. Eligible patients had histologically confirmed metastatic breast cancer with measurable disease by Response Evaluation Criteria in Solid Tumors (RECIST), and adequate hematopoietic, renal, and hepatic function. Ixabepilone 8 mg/m²/day was given intravenously daily for 3 days for the first 3-week cycle and increased to 10 mg/m²/day for subsequent cycles if patients did not have hematologic or other toxicity after the first cycle. Patients continued treatment until progressive disease or unacceptable toxicity. Three, 29, and 33 of 65 cycles administered were at the 7 mg/m², 8 mg/m² and 10 mg/m² dose levels respectively. Grade 4 leukopenia (n=1), grade 3 neutropenia (n=2), grade 2 neuropathy (n=3), and grade 2 transaminase elevation (n=2) were the most notable toxicities. Ten patients had stable disease for at least 6 weeks. No complete or partial responses were observed in 12 evaluable patients treated with ixabepilone daily for 3 days. Although ixabepilone was well-tolerated, the dose of 8–10 mg/m² daily for 3 days is not an effective therapy in metastatic breast cancer previously exposed to taxanes.