 Patients undergo tumor resection or biopsy and have microdialysis catheter placed on day 0. Beginning at least 24 hours later, patients receive eribulin mesylate intravenously IV over 2-5 minutes on day 1. Serial brain fluid samples are collected for approximately 72 hours and the microdialysis catheter is then removed. Beginning at least 2 weeks after tumor resection or biopsy, patients may continue to receive eribulin mesylate IV over 2-5 minutes on days 1 and 8. Courses repeat every 21 days in the absence of disease progression or unacceptable toxicity. 