GSTP1 and prostate cancer: The visualisation of methylation at GSTP1 in the WGBS cohort provides a clear illustration of the reason that GSTP1 promoter methylation performs so well as a highly specific diagnostic marker of prostate cancer (e.g., previous works15, 26): the locus is almost entirely unmethylated in normal tissue, and methylated in all tumour tissue, at a range of levels.