Premalign özellikli prostat dokularında epigenetik değişikliklerin karakterizasyonu

Prostate cancer (PCa) is one of the most commonly diagnosed, non-cutaneous malignancy and a leading cause of cancer-related death worldwide. Conventional methods of diagnosis include prostate specific antigen testing, digital rectal examination, and transrectal ultrasound guided prostate biopsies. The limitation of these approaches has led to the development of multiparametric MRI (mpMRI) guided biopsies. Significantly more sensitive, mpMRI can accurately identify radiographically suspicious lesions that are likely to be malignant and guide biopsy collection. However, even with this approach, ~10% of suspicious biopsies are found to be histopathologically benign. Given the sensitivity of mpMRI, it is unclear if these lesions harbor premalignant features or are technical artifacts. Epigenetic alterations, including DNA hypermethylation, are commonly found early in the development of PCa. Therefore, using these as premalignant markers, we characterized the epigenetic signatures of those radiographically suspicious lesions that were deemed to be benign by histology. Focusing on three well-characterized tumor suppressors, APC, GSTP1 and RARβ2 we developed a highly sensitive quantitative methylation specific PCR method to quantify promoter methylation. This method could robustly identify malignant and benign samples with the limited genetic material from FFPE biopsies. With this we quantified the promoter methylation of radiographically suspicious lesions from patients with either histopathology positive ("malignant"; n=28, 82 biopsies) or negative ("MRI"; n=18, 56 biopsies) biopsies. We found that the observed methylation levels of MRI cohort were markedly higher than benign samples yet lower than malignant tumors. This difference was highly gene specific. In our MRI cohort we did not observe any methylation positive cores at the APC promoter while almost all samples were positive for GSTP1 methylation. Even in the malignant cohort, only 37% of biopsies were methylation positive with the APC gene. Further, the relative methylation of the MRI cohort was heterogeneous with several cores biopsied from the same patient being positive for different markers. Intriguingly, when we investigated the clinical outcome of this cohort, almost none of the lesions in the MRI cohort had progressed into a neoplastic lesion. Overall, our results demonstrate that radiographically suspicious non-malignant lesions carry premalignant epigenetic alterations.