Quantitation of GSTP1 Methylation in Non-neoplastic Prostatic Tissue and Organ-Confined Prostate Adenocarcinoma

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Abstract
Background: Methylation of regulatory sequences near GSTP1, which encodes the π class glutathione S-transferase, is the most common epigenetic alteration associated with prostate cancer. We determined whether the quantitation of GSTP1 methylation in histopathologically distinct prostate tissue samples could improve prostate cancer detection. Methods: We used a fluorogenic real-time methylation-specific polymerase chain reaction (MSP) assay to analyze cytidine methylation in the GSTP1 promoter in prostate tissue samples from 69 patients with early-stage prostatic adenocarcinoma (28 of whom also had prostatic intraepithelial neoplasia lesions) and 31 patients with benign prostatic hyperplasia. The relative level of methylated GSTP1 DNA in each sample was determined as the ratio of MSP-amplified GSTP1 to MYOD1, a reference gene. We also performed a prospective, blinded investigation to quantitate GSTP1 promoter methylation in sextant prostate biopsy specimens from 21 additional patients with elevated serum prostate-specific antigen levels, 11 of whom had histologically identified adenocarcinoma and 10 of whom had no morphologic evidence of adenocarcinoma. All data were analyzed by using nonparametric two-sided statistical tests. Results: The median ratios (and interquartile ranges) of MSP-amplified GSTP1 to MYOD1 in resected benign hyperplastic prostatic tissue, intraepithelial neoplasia, and adenocarcinoma were 0 (range, 0–0.1), 1.4 (range, 0– 45.9), and 250.8 (range, 53.5–697.5), respectively; all of these values were statistically significantly different (P<.001). The median ratios of MSP-amplified GSTP1 to MYOD1 in the prospectively collected sextant biopsy samples were 410.6 for the patients with adenocarcinoma and 0.0 for the patients with no evidence of adenocarcinoma (P<.001). Conclusion: Quantitation of GSTP1 methylation accurately discriminates between normal hyperplastic tissue and prostatic carcinoma in small samples of prostate tissue and may augment the standard pathologic/histologic assessment of the prostate.