Abstract B16: Detection of prostate cancer associated DNA hypermethylation in diagnostic needle biopsies: Insight into field effects and heterogeneity

Prostate cancer (PC) is the fifth leading cause of cancer deaths among men worldwide and the second most common cancer form with an estimated 1.1 million diagnoses in 2012. Diagnosis is based on histological evaluation of needle biopsies by a trained pathologist. Despite the high number of diagnoses, PC is frequently missed in the initial set of biopsies. Thus, in more than 15 % of patients with initial negative biopsies, PC is found in repeat biopsies. The aim of this project is to evaluate if DNA methylation-based cancer field effects can be detected in cancer-negative prostate biopsy samples for the nine genes HAPLN3, AOX1, GAS6, KLF8, MOB3B, CCDC181 (C1orf114), GABRE, SLC18A2, and GSTP1, and if this could be a potential novel diagnostic tool. Hypermethylation of these genes is known to be strongly associated with PC in prostatectomy specimens. First, we confirmed the presence of hypermethylation of all genes in malignant (n=48) compared to non-malignant biopsy tissue samples (n=40) using quantitative methylation specific PCR (pBonferroni≤0.00002 in Mann Whitney U test, AUC range 0.80-0.98 in ROC analysis). Next, non-malignant biopsy samples from men with (n=39) or without (n=40) cancer in other biopsies were compared. Here, the methylation status of no single gene showed a significant correlation to the presence of PC in other biopsies. However, PC is a heterogeneous disease and a panel of markers could lead to increased sensitivity for PC if each marker adds little but complementary information. Indeed, a 4-gene model (HAPLN3/GSTP1/AOX1/SLC18A2) was able to separate the 2 groups of non-malignant samples with an AUC of 0.65 in ROC analysis (PPV = 100 %, NPV = 59.7 %), indicating the existence of an epigenetic cancer field effect. In our sample set, this corresponds to 12 out of 39 samples that would be identified as originating from PC patients based on the molecular analysis although no signs of malignancy were identified by pathology. Finally, to investigate epigenetic field effects and heterogeneity on a genomewide scale, we have analyzed multiple cancer foci, adjacent non-malignant and distant non-malignant samples from radical prostatectomy specimens from each of 4 patients with multifocal PC using the Infinium HumanMethylation450 BeadChip (Illumina). The results will be presented at the conference. In summary, PC-specific hypermethylation of all nine genes was confirmed in diagnostic needle biopsies. Furthermore, DNA methylation based cancer fiel