Epigenetic field effects: Potential applications for detection of occult high-grade prostate cancer.
20 Background: Needle biopsy (Bx) pathology is central to the diagnosis and management of prostate cancer (PCa), but Bx sampling error can result in an underestimate of Gleason grade (GS). Epigenetic DNA hypermethylation markers associated with PCa are commonly observed in histologically benign tissue adjacent to a cancer focus. Such field effects are the basis for a diagnostic test in which the absence of GSTP1, APC and RASSF1 hypermethylation in benign Bxs is associated with a low risk of “missed” PCa. Relatively low methylation thresholds are used for the current epigenetic test (ConfirmMDx) that is designed to be sensitive to any occult cancer, regardless of GS. We are evaluating new prototype epigenetic tests that are designed to be sensitive to the GS of an occult PCa. Methods: DNA was extracted from prostate bx tissue prints and used for quantitative methylation-specific PCR for GSTP1, APC and RASSF1. Results were computed as levels of marker methylation relative to a common reference gene. Each of 12 cores was tested from a series of 102 Bx patients: 20 diagnosed with no cancer (Group 1), 46 with GS 6 PCa (Group 2) and 36 with GS 7 PCa (Group 3). Results: For all 3 markers, we observed a positive correlation between the highest level of hypermethylation in the benign cores and in the same-patient cancer cores. This correlation was strongest for APC (P &lt;0.0001). For GSTP1 and APC, hypermethylation intensity in the benign cores was also positively correlated with the overall GS. Interestingly, for each marker, the GS 6 cores from Group 3 (overall diagnosis GS 7) showed significantly higher levels of hypermethylation than the GS 6 cores from Group 2 (overall GS 6). The strongest correlation between the level of GS 6 core hypermethylation and overall GS was observed for GSTP1(P=0.0002). Conclusions: For GSTP1, APC and RASSF1, the intensity of field effect hypermethylation in benign Bx cores was positively correlated with the level of hypermethylation present in the cancer cores from the same patient. In GS 6 cancer cores, the intensity of hypermethylation is higher in subjects who also have cores of GS 7 than in subjects with GS 6 cores only. Both findings support the feasibility of an epigenetic test that is sensitive to the GS of an occult PCa.