ERIBULIN MESYLATE (HALAVEN®) is a microtubule dynamics inhibitor. It is a synthetic analog of halichondrin B, a product isolated from the marine sponge Halichondria okadai. ERIBULIN MESYLATE (HALAVEN®) inhibits the growth phase of microtubules without affecting the shortening phase and sequesters tubulin into nonproductive aggregates. It exerts its effects via a tubulin-based antimitotic mechanism leading to G2/M cell-cycle block, disruption of mitotic spindles, and, ultimately, apoptotic cell death after the prolonged mitotic blockage. ERIBULIN MESYLATE (HALAVEN®) is indicated for the treatment of patients with metastatic breast cancer who have previously received at least two chemotherapeutic regimens for the treatment of metastatic disease. It is also indicated for the treatment of patients with unresectable or metastatic liposarcoma who have received a prior anthracycline-containing regimen.