Minimally invasive
follicular thyroid carcinoma (MI-
FTC) is characterized by limited capsular and/or vascular invasion with good long-term outcomes. However, some cases of MI-
FTC show a poor prognosis because of severe distant
metastasis (i.e., metastatic MI-
FTC). Nonetheless, no method has been established for predicting the prognosis of MI-
FTC. This study was conducted to identify novel prognostic factors for metastatic MI-
FTC by the use of
microRNA (
miRNA). Thirty-four patients with MI-
FTC were categorized into two groups: the metastatic group, M(+) (n=12) and the non-metastatic group, M(-) (n=22). In the M(+) group, distant
metastasis was recognized after the initial operation established the diagnosis of MI-
FTC. In the M(-) group, no distant
metastasis was recognized postoperatively for ≥ 10 years. Using
laser microdissection followed by quantitative real-time PCR and PCR arrays, we performed a comprehensive expression profiling of 667
miRNAs in
formalin-fixed,
paraffin-embedded samples from the initial MI-
FTC operation. Furthermore, we assessed the potential use of
miRNAs as novel
biomarkers for the metastatic potential of MI-
FTC by logistic regression analysis. Comprehensive quantitative analysis of
miRNA expression in MI-
FTC samples revealed that the miR-221/222 cluster (i.e., miR-221, miR-222 and miR-222*), miR-10b and miR-92a were significantly upregulated in the M(+) group compared with the M(-) group. Interestingly, the expression levels of these
miRNAs were also shown to be upregulated in widely invasive
FTC (WI-
FTC; n=13) that has distant
metastasis and worse prognosis, indicating a close similarity in the
miRNA expression between metastatic MI-
FTC and WI-
FTC. Logistic regression analysis revealed that miR-10b made a significant contribution to prognosis (OR 19.759, 95% CI 1.433-272.355, p=0.026). Our findings suggest that miR-10b is a potential prognostic factor for evaluating the metastatic potential of MI-
FTC at an initial operation stage.