285: MicroRNA expression in triple-negative versus other subtypes of breast cancer

Background: Breast cancer is a clinically, morphologically, and genetically heterogeneous disease thus requiring a personalized approach to the treatment. Currently used biomarkers are not enough informative to predict the pace or the outcome of the disease, therefore new markers are required. One of such potential biomarker is microRNA: a class of small, non-coding molecules that regulate gene expression at a post-transcriptional level. In malignancies, expression of the microRNAs is altered and correlates with the clinical features of the disease. This study attempted to explore some microRNA expression differences in a more aggressive subtype (triplenegative) compared to other breast cancer subtypes (luminal-A, luminal-B, and HER2+). Material and Methods: The study group consisted of 13 LA, 7 LB, 2 HER2+, and 50 TN breast cancer tissues. MicroRNAs were extracted from the formalinfixed and paraffin embedded tumor tissues. A quantitative analysis of miR-10b, miR-21, miR-29a, miR-31, and miR-214 in cancer tissues was performed by real-time PCR. RNU6B was used as an internal control. All cancer tissues contained more than 50% of cancer cells per sample. A disease-specific survival was calculated from the date of the diagnosis to the date of the death from the cancer. The median follow-up period of breast cancer patients was 47 months. The disease-specific survival was analyzed using a Log-rank (Mantel- Cox) test. Statistical significance was set at the 95% level (p < 0.05). Results: Expression of miR-21, miR-31, and miR-214 was higher in TN than in other tumor tissues (p = 0.0027; p = 0.0012; p = 0.0230, respectively). No statistically significant differences in miR-10b and miR-29a expressions between TN and other subtypes were observed (p = 0.1902 and p = 0.1707, respectively). Breast cancer patients with the high expression of miR-31 and miR-214 showed a non-significant trend for a worse disease-free survival than patients with the low expression (p = 0.1707 and p = 0.2220, respectively). No statistically significant difference in regard of high and low miR-21 expression was observed (p = 0.3170). Conclusion: Different microRNA expression in distinct subtypes of breast cancer reflects genetic heterogeneity of breast cancer and indicates outcome of the disease; breast cancer patients with the high expression of miR-31 and miR-214 have a non-significantly worse disease-free survival than patients with the low expression. No conflict of interest