Total RNA was extracted from tumors and from contralateral normal adjacent thyroid, from which frozen samples were available (n = 84), using a TRIzol commercial kit (Thermo Scientific/GIBCO) according to the manufacturer’s protocol. RNA was quantified by spectrophotometry, and its quality was checked by analysis of 260/280 nm and 260/230 nm ratios. For cDNA preparation, 1 μg of total RNA was reverse-transcribed using the RevertAid first-strand cDNA synthesis kit (Thermo Scientific/Fermentas).