Glioblastoma multiforme (GBM), the most common malignant brain tumor of adults, 
is relatively rare in children. In a GBM affecting a 16-year-old boy, the tumor 
spread across the corpus callosum (butterfly glioma). This type of bilateral 
hemispheric growth has previously been thought to result from spread along the 
white matter tracts. Two samples obtained from opposite sides of the same tumor 
were analyzed comprehensively for loss of heterozygosity (LOH) and 
microsatellite instability (MSI). Amplification of EGFR and MDM2 was studied by 
means of multiplex polymerase chain reaction. Exons 5, 6, 7, and 8 of TP53 were 
screened for mutations by sequencing. In neither specimen were molecular 
alterations found in the EGFR, MDM2, or TP53 genes. The specimen obtained from 
the right hemisphere exhibited a high level of MSI and LOH in chromosome arms 
5q, 9p, and 13q. The specimen from the left hemisphere exhibited LOH in 
chromosome arms 3p, 5q, 9p, 9q, 10p, 10q, and 13q. Here we propose four 
plausible hypothetical scenarios underlying the tumorigenesis of this GBM.