The following copy number abnormalities were all most common in the glioblastomas; polysomy of chromosome 7 (64%); focal amplification of the region encompassing the EGFR receptor gene (44%); homozygous deletion of the 9p21.3 region encompassing the CDKN2A/14ARF and CDKN2B genes (32%); monosomy chromosome 10 (65%); amplifications of 12q14-15 region encompassing the CDK4 (11%) and MDM2 (9%) genes; loss of the region encompassing the RB1 gene (27%); and trisomy 19 (21%). This evidence concerns the gene RB1 and glioblastoma.