For example, DNA hypermethylation of the glutathione S-transferase pi 1 (GSTP1) gene was correlated with prostate cancer (Esteller et al., 1998), thus serving as a diagnostic tool, while hypermethylation of O 6-methylguanine-DNA methyltransferase (MGMT) aids in decisions for therapeutic strategies for glioma (Esteller et al., 2000). Here, MGMT is linked to central nervous system cancer.