On November 15, 2010, the U.S. Food and Drug Administration (FDA) announced that Halaven (eribulin mesylate) has been approved for the treatment of patients with metastatic breast cancer who have been treated with at least 2 previous advanced chemotherapy regimens. Halaven is a synthetic formulation of a chemotherapeutically active compound derived from the black soft sponge (Halichondria okadai). The injectable drug is a microtubule inhibitor that inhibits the growth of cancer cells. Prior to treatment with Halaven, patients should receive previous anthracycline-based and paclitaxel-based chemotherapy regimens for early or advanced breast cancer. The safety and efficacy of Halaven was confirmed in a single study involving 762 women with metastatic breast cancer who had been treated with at least 2 previous chemotherapy regimens for advanced disease and who were randomly assigned to receive either the Halaven treatment group or a different monotherapy group chosen by their oncologist. The median overall survival time was 13.1 months in the Halaven group compared to 10.6 months in the monotherapy group. The most common adverse reactions with Halaven included neutropenia, anemia, leukopenia, alopecia, fatigue, nausea, weakness, constipation, and peripheral neuropathy.