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Summary Introduction. MicroRNAs are a class of small, non-coding RNA molecules able to regulate gene expression at the post-transcriptional level through binding to the 3’-UTR of the targeted mRNA, thus suppressing translation of the mRNA. In various diseases, including malignancies, expression of microRNAs is altered. Moreover, the altered expression of the microRNAs correlates with clinical and pathophysiological features of cancer thus making them good candidates for prognostic/predictive markers. Aim of the study. The aim of this study was to determine expression level of five different microRNAs (miR-10b, miR-21, miR-29a, miR-31, and miR-214) in breast cancer tissues and to look for the differences in microRNA expression between distinct subtypes of breast cancer. Material and methods. Forty five breast cancer and corresponding resection line tissues (control tissues) were studied. Breast cancer tissues were classified into the subtypes of triple-negative (23), luminal-A (13), luminal-B (7), and HER2+ (2). Quantitative analysis of miR-10b, miR-21, miR-29a, miR-31, and miR-214 was performed by real-time PCR. The expression levels of microRNAs were normalized by the expression of the reference gene RNU6B. The event-free survival in regard of high and low expression levels of microRNAs were analyzed by Log-rank (Mantel Cox) and Gehan-Breslow-Wilcoxon tests. Results. Expression levels of four microRNAs (miR-21, miR-29a, miR-31, and miR-214) were significantly higher in cancer tissues than in corresponding resection line tissues. Breast cancer patients with low expression level of miR-21 showed a trend of better event-free survival than breast cancer patients with high expression level of miR-21; however, this trend did not reach statistical significance. In triple-negative tumor tissues, miR-21, miR-29a, and miR-31 showed significantly higher expression level than in luminal-A tumor tissues. Expression levels of miR-21 and miR-29a were significantly higher in triple-negative tumor tissues than in luminal-B tumor tissues. Conclusions. Breast cancer patients with high expression level of miR-21 in tumor tissues show a trend of worse event-free survival, though; this trend did not reach statistical significance. Different microRNA expression in distinct subtypes of breast cancer points to the genetic heterogeneity of breast cancer, different regulatory targets and signaling pathways |
