miR-146b is Highly Expressed in Adult Papillary Thyroid Carcinomas with High Risk Features Including Extrathyroidal Invasion and the BRAFV600E Mutation

Background: Papillary thyroid carcinoma (PTC) are clinicopathogenetically heterogeneous. Micro-RNAs (miRNAs) are involved in the pathogenesis of diverse human cancers, including PTC. Information regarding associations between clinicopathological features of PTC with the expression of specific miRNAs, however, is sparse. In this study, we compared expression of deregulated miRNAs in PTCs to assess this was associated with selected clinicopathogenetic features. Methods: We analyzed the expression levels of three reported deregulated miRNAs (miR-221, miR-222, and miR-146b) using quantitative real-time polymerase chain reaction in 100 cases of PTCs with distinct clinicopathogenetic characteristics and 16 paired normal controls. The tumor samples were categorized into low- and high-risk groups on the basis of the tumor-node-metastasis staging system. Results: The expression levels of miR-221, miR-222, and miR-146b were significantly associated with extrathyroidal invasion (p = 0.013, 0.05, and 0.003, respectively). The expression levels of miR-221 and miR-146b were significantly higher in the high-risk PTC group (p = 0.01 and 0.042, respectively). The miR-146b expression levels in PTCs with BRAF mutation were significantly higher than those without this mutation (p < 0.0001). There were no other associations between the expression of these miRNAs and other clinicopathological parameters. Conclusions: Our results show the potential importance of miR-221, miR-222, and miR-146b in determining the aggressive properties of PTCs and highlight the need to identify the gene targets of these miRNAs.