Glioblastomas, the most frequent malignant brain tumor in adults, are widespread in the brain, despite their discrete appearance on computed tomography (CT) or magnetic resonance imaging (MRI). While this tumor tends to spread widely in the brain, unlike other tumors of the body, it rarely metastasizes, or spreads, to other organs. Approximately 10 percent of patients with glioblastoma develop metastatic disease after radiation or brain surgery. In the absence of radiation or brain surgery, few patients have developed disease spread outside the brain.