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.