Patients with cancers exhibit differential MDM2 and p53 protein expression in gliomas and breast cancers, which contain the G and/or T alleles of SNP309 (Tsuiki et al., 2007; Krekac et al., 2008), and differential p16INK4a protein expression in gastric cancers in the absence of methylation (Tsujie et al., 2000). Here, MDM2 is linked to central nervous system cancer.