Halaven (generic name: eribulin mesylate) is a prescription medication used in the treatment of certain types of cancer, most notably metastatic breast cancer and liposarcoma, a rare type of cancer that arises in fat cells. It belongs to a class of drugs known as microtubule inhibitors, which work by inhibiting the growth and spread of cancer cells. Halaven is administered through an injection into a vein (intravenously) by a healthcare professional. It is specifically designed for patients who have already undergone certain other cancer treatments without success. As with any cancer therapy, Halaven comes with a range of potential side effects, and its use is carefully considered by healthcare providers based on the individual patient's health status and medical history.