Quantitative GSTP1 methylation levels correlate with Gleason grade and tumor volume in prostate needle biopsies

Purpose: Methylation of the GSTP1 gene promoter region is the most common epigenetic change in prostate cancer. The quantitative GSTP1 methylation assay, a recently developed methylation specific and polymerase chain reaction based technique, allows the accurate discrimination of benign prostate tissue and prostate cancer even in small, formalin fixed prostate needle biopsies. In this study we investigated whether GSTP1 methylation correlated with Gleason grade and tumor volume in prostate biopsies. We also compared quantitative GSTP1 methylation with the histological diagnosis in each biopsy. Materials and Methods: Formalin fixed, paraffin embedded prostate needle cores (25 mu) were used for the GSTP1 methylation study. After excluding 98 prostate needle cores (47%) with insufficiently extracted DNA 109 biopsies from 40 patients with prostate cancer of various Gleason grades and tumor volume, and benign prostate tissue were tested for GSTP1 methylation using quantitative fluorogenic real-time methylation specific polymerase chain reaction. Results: A total of 13 benign and 96 cancer biopsy parts were included in this study. GSTP1 methylation was positive (GSTP1-to-ACTB ratio 5 or greater) in 83 of 96 cancer parts (86.5%). All 13 benign parts (100%) were negative for GSTP1 methylation with a methylation level of 0 in 12 and 1 in 1. The sensitivity and specificity of quantitative GSTP1 methylation assay were 86.5% and 100%, respectively. Quantitative GSTP1 methylation correlated with Gleason grade, demonstrating higher GSTP1 methylation in higher Gleason grade tumors (Spearman correlation coefficient 0.377, p < 0.0001). Likewise, GSTP1 methylation also correlated with the cancer percent per biopsy (Spearman correlation coefficient 0.567, p < 0.0001). A multiple linear regression model predicted the greater contribution of cancer percent than Gleason grade to quantitative GSTP1 methylation levels. Conclusions: We confirmed that the quantitative GSTP1 methylation assay reliably discriminates benign and malignant prostate tissues, thus, augmenting the routine histological evaluation of prostate needle biopsies. In addition, quantitative GSTP1 methylation also correlated with prostate cancer Gleason grade and cancer volume, suggesting that quantitative GSTP1 methylation may be of prognostic significance.