Eisai Co Ltd is developing eribulin, a simplified synthetic macrocyclic ketone analog of the tubulin inhibitor halichondrin B, for the potential treatment of cancer. Phase III trials are underway in the US and Europe for patients with breast cancer. Eribulin is currently in phase II trials for NSCLC and soft tissue sarcoma, and pancreatic, prostate, ovarian, fallopian tube, peritoneal and head and neck cancer, and phase I/II trials for urothelial cancers.