Eribulin mesylate is a methanesulfonate salt obtained by reaction of eribulin with one equivalent of methanesulfonic acid. A fully synthetic macrocyclic ketone analogue of marine sponge natural products. Inhibits growth phase of microtubules via tubulin-based antimitotic mechanism, which leads to G2/M cell-cycle block, disruption of mitotic spindles, and, ultimately, apoptotic cell death after prolonged mitotic blockage. It has a role as an antineoplastic agent and a microtubule-destabilising agent. It contains an eribulin(1+).