Kurebayashi et al. [24] showed an increase of Tg mRNA in human poorly differentiated papillary thyroid carcinoma cell line (KTC-1) after incubation with 1 μmol/l all-trans-retinoic acid for 24 hours; however, others performing similar experiments have reported unchanged Tg mRNA expression [25]. This evidence concerns the gene TG and thyroid gland papillary carcinoma.