The study investigates the role of microRNAs (miRNAs) in papillary thyroid carcinoma (PTC). It was found that numerous miRNAs are up-regulated in PTC tumors compared to unaffected thyroid tissue, with a set of five miRNAs (miR-221, -222, and -146) showing significant upregulation. MiR-221 was also upregulated in unaffected thyroid tissue in several PTC patients, suggesting an early event in carcinogenesis. Tumors with strong upregulation of these miRNAs showed a dramatic loss of KIT transcript and protein. In five out of ten cases, this downregulation was associated with germline single-nucleotide changes in the KIT recognition sequences. The study concludes that miRNA upregulation and regulation of KIT are involved in PTC pathogenesis, and that sequence changes in genes targeted by miRNAs can contribute to their regulation.The study investigates the role of microRNAs (miRNAs) in papillary thyroid carcinoma (PTC). It was found that numerous miRNAs are up-regulated in PTC tumors compared to unaffected thyroid tissue, with a set of five miRNAs (miR-221, -222, and -146) showing significant upregulation. MiR-221 was also upregulated in unaffected thyroid tissue in several PTC patients, suggesting an early event in carcinogenesis. Tumors with strong upregulation of these miRNAs showed a dramatic loss of KIT transcript and protein. In five out of ten cases, this downregulation was associated with germline single-nucleotide changes in the KIT recognition sequences. The study concludes that miRNA upregulation and regulation of KIT are involved in PTC pathogenesis, and that sequence changes in genes targeted by miRNAs can contribute to their regulation.