GSTP1 (glutathione-S-transferase, pi 1), also called GST3/DFN7, is a family of enzymes that play an important role in detoxification by catalyzing the conjugation of many hydrophobic and electrophilic compounds with reduced glutathione. GSTP1 act like a tumor suppressor gene, which when inactivated leads to tumor growth, and the -class glutathione S-transferase is commonly inactivated by somatic CpGisland hypermethylation in cancers of the prostate, liver, and breast. Methylation of regulatory sequences at the GSTP1 gene locus is found in the vast majority (>90%) of prostate carcinomas and is associated with transcriptional down-regulation.