Five recently reported phase II trials have shown that ixabepilone, an epothilone B analog, is effective against metastatic breast cancer and non-small-cell lung cancer (NSCLC). Ixabepilone has been designed to optimize the properties of the natural product epothilone B. Epothilone drugs have a mechanism of action similar to that of taxanes (docetaxel and paclitaxel): they cause mitotic arrest by stabilizing microtubules but bind to different sites on tubulin than taxanes.

Four of the trials examined different groups of patients with metastatic breast cancer. Denduluri et al. examined ixabepilone in 23 patients previously untreated with taxanes; 13 (57%) had partial responses, and the median response duration was 5.6 months. In 65 patients previously treated with anthracyclines, Roché et al. found a 41.5% response rate, and a median response duration of 8.2 months. Two trials examined patients with drug resistant tumours. Thomas et al. studied 49 patients resistant to taxanes and saw a median response duration of 10.4 months and a 12% response rate. The responses were all partial, but 5 of 6 patients who responded had not responded to taxanes before, indicating that ixabepilone can work in patients who don't respond to taxanes. Finally, Perez et al. examined 113 patients resistant to an anthracycline, a taxane and capecitabine chemotherapy and saw an 11.5% response rate and a median response duration of 5.7 months.

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