Eribulin mesylate is a synthetic analog of halichondrin B (a polyether macrolide isolated from a marine sponge). It is a nontaxane microtubule dynamics inhibitor with a novel mechanism of action. It is the first drug that has demonstrated an improvement in overall survival as a single agent compared with the physician's choice of currently available treatments in locally advanced or metastatic breast cancer, previously treated with anthracyclines and taxanes. It has shown a good manageable tolerability profile. This drug has been approved by the US FDA and by the EMA for patients with locally advanced or metastatic breast cancer who have received at least two chemotherapeutic regimens for advanced/metastatic disease. Prior therapy should have included an anthracycline and a taxane in either the adjuvant or metastatic setting unless patients were not suitable for these treatments. The aim of this article is to describe the mechanism of action, pharmacokinetics, pharmacodynamics and the most relevant clinical trials in the development of this drug.