The aim of this study was to determine the safety, maximum tolerated dose (MTD), recommended phase II dose, and efficacy of the epothilone B analogue ixabepilone plus capecitabine in anthracycline-pretreated/ resistant and taxane-resistant metastatic breast cancer (MBC).

A total of 106 patients were enrolled. The study consisted of a dose-escalation phase (phase I) and a tumor response rate evaluation phase (phase II). Seventy-four patients were treated in phase I with schedule A (ixabepilone 40 mg/m2 intravenously on day 1 plus capecitabine 1650-2000 mg/m2 on days 1-14 of a 21-day cycle) or schedule B (ixabepilone 8-10 mg/m2 on days 1-3 plus capecitabine 1650 mg/m2 on days 1-14 of a 21- day cycle).

No dose-limiting toxicities (DLTs) were observed in the 8/1650 mg/m2 and 10/1650 mg/m2 cohorts; 1 of 30 patients in the 40/1650 mg/m2 cohort and 2 of 30 patients in the 40/2000 mg/m2 cohort had a DLT consisting of grade 3 plantar-palmar erythrodysesthesia (PPE). The 40/2000 mg/m2 dose was defined as the MTD for schedule A, and a total of 62 patients were treated for the phase II portion of the trial, which examined tumor response. The objective response rate was 30%, median time-to-response was 6 weeks, median duration of response was 6.9 months, and median progression-free survival was 3.8 months. Grade 3/4 treatment-related events in phase II included fatigue (34%), PPE (34%), myalgia (23%), nausea (16%), peripheral neuropathy (19%), and diarrhea/vomiting (10%). Grades 3/4 neutropenia (69%) and leukopenia (55%) were managed primarily by dose reduction/treatment interruption.

Ixabepilone plus capecitabine demonstrated clinical activity and an acceptable safety profile in patients with anthracycline-pretreated/resistant and taxane-resistant MBC. Ixabepilone was recently approved in the United States for the treatment of resistant/refractory locally advanced or MBC.