GSTP1 and prostate intraepithelial neoplasia: Methylation of the GSTP1 gene promoter has been the most frequently detected epigenetic alteration, and occurs in over 90% of cancerous samples and about 70% of prostatic intraepithelial neoplasia (PIN) samples [41, 42], but is rarely detected in normal prostate or benign prostatic hyperplasia (BPH) tissues.