Avastin is the experimental drug being administered in this research study. Avastin binds a protein called vascular endothelial growth factor, or VEGF. VEGF is produced by tumors and circulates in the blood. One of VEGF's main roles is to support the growth of new blood vessels. During cancer, VEGF promotes the growth of blood vessels that bring nutrients to tumor cells and help them grow. Avastin binds to VEGF, which then prevents VEGF from functioning. In laboratory studies, Avastin prevented the growth of several different types of cancer cells grown in animals. Avastin was approved by the Food and Drug Administration (FDA) for the treatment of metastatic colorectal cancer in combination with chemotherapy. Avastin has not been approved by the FDA for the treatment of GBM and is, therefore, considered experimental. Avastin is currently undergoing testing (alone and in combination with another anti-cancer drug, irinotecan) in persons with GBM that have come back after conventional treatment.