CDKN2A and cancer: Deregulation of the p53 tumor suppressor occurs in >85% of primary glioblastomas in the form of p53 gene mutations (35%) or homozygous deletion of the p16Ink4/ARF locus (60%), while amplification of the MDM homologs 1/2/4 has been observed in 14% of patients with this cancer type [8,9,10,11,12,13].