Patients undergo blood collection for blood typing (if not already obtained) and factor VIII and C-reactive protein levels at baseline. Patients are followed to obtain information on their Karnofsky performance status, treatment they receive for their brain tumor, and occurrence of any thrombotic events (e.g., pulmonary embolism or deep-vein thrombosis). Patients are followed every 28 days until the development of thrombotic events, after which they are followed every 2 months for survival.