Heterogeneity of miRNA expression in localized prostate cancer with clinico-pathological correlations

Ahmed Hussein Zedan (1,2), Søren Garm Blavnsfeldt (1), Torben Frøstrup Hansen (2), Boye Schnack Nielsen (3), Niels Marcussen (4), Mindaugas Pleckaitis (5), Palle Jörn Sloth Osther (1,6), Flemming Brandt Sørensen (5,6)

1) Urological Research Center, Department of Urology, Vejle Hospital, part of Lillebaelt Hospital,  Vejle, Denmark. 2) Department of Oncology, Vejle Hospital, part of Lillebaelt Hospital, Vejle, Denmark. 3) Bioneer A/S, Hørsholm, Denmark. 4) Department of Pathology, Odense University Hospital, Odense, Denmark. 5) Department of Clinical Pathology, Vejle Hospital, part of Lillebaelt Hospital, Vejle, Denmark. 6) Institute of Regional Health Research, University of Southern Denmark, Denmark.

In the last decade microRNAs (miRNAs) have been widely investigated in prostate cancer (PCa) and have shown to be promising biomarkers in diagnostic, prognostic and predictive settings. However, tumor heterogeneity may influence miRNA expression. The aims of this study were to assess the impact of tumor heterogeneity, as demonstrated by a panel of selected miRNAs in PCa, and to correlate miRNA expression with risk profile and patient outcome.

Materials and methods
Prostatectomy specimens and matched, pre-operative needle biopsies from a retrospective series of 49 patients, who underwent curatively intended surgery for localized PCa, were investigated with a panel of 6 miRNAs (miRNA-21, miRNA-34a, miRNA-125b, miRNA-126, miRNA-143 and miRNA-145), using tissue micro-array (TMA) and in situ hybridization (ISH). Inter-and intra-patient variation was assessed using intra-class correlation (ICC). 

Four miRNAs (miRNA-21, miRNA-34a, miRNA-125 and miRNA-126) were significantly upregulated in PCa compared to benign prostatic hyperplasia (BPH), and except for miRNA-21 these miRNAs documented a positive correlation between the expression level in PCa cores compared to their matched BPH cores, (r > 0.72). The ICC varied from 0.451 to 0.764, with miRNA-34a showing an intra-tumoral heterogeneity accounting for less than 50% of the total variation. Regarding clinico-pathological outcomes, only miRNA-143 showed potential as a prognostic marker, with a higher expression correlating with longer relapse-free survival (p = 0.016). 

The present study documents significant upregulation of the expression of miRNA-21, miRNA-34a, miRNA-125 and miRNA-126 in PCa compared to BPH, and suggests a possible prognostic value associated with the expression of miRNA-143. The results document, however, intra-tumoral heterogeneity in the expression of various miRNAs, calling for caution in using these tumor-tissue biomarkers in prognostic and predictive settings.