CDKN1B and thyroid cancer, nonmedullary, 2: Considering that both FTC and PTC are differentiated thyroid carcinomas originating from a common cell type (the follicular cell), the upregulation of miR-221 and miR-222 in MI-FTC may lead to dysregulated cell cycle progression by targeting CDKN1B and CDKN1C and facilitates its hematogenous metastasis to lung and bone.