Beyond taxanes: the next generation of microtubule-targeting agents

Taxanes are a standard first-line option for metastatic breast cancer (MBC), but their utility may be limited by primary or acquired resistance. New microtubule-targeting agents have been developed to overcome taxane resistance and provide additional options for improving patient outcomes. This article reviews these alternative microtubule-targeting agents and their potential clinical benefits for MBC patients. Relevant clinical data were compiled through searches within PubMed and congress abstract databases. Ixabepilone, a novel microtubule-stabilizing drug approved by the US Food and Drug Administration (FDA), has proven efficacy across multiple lines of therapy, including patients with taxane-resistant/refractory disease. In phase III trials, ixabepilone plus capecitabine significantly improved progression-free survival compared with capecitabine alone in anthracycline/taxane-pretreated patients. Eribulin has recently been approved by the FDA and by the European Medicines Agency for the treatment of patients with MBC who have received at least two prior chemotherapy regimens for late-stage disease. In a phase III trial, eribulin extended overall survival compared with the physician's treatment choice in heavily pretreated MBC patients. In addition, several investigational microtubule-targeting agents may have therapeutic potential in MBC. The development of new microtubule-targeting agents helps to address the need for additional effective regimens for patients progressing after standard treatment with anthracycline- and taxane-containing regimens.