DIO2 and cancer: We previously evaluated the role of thyroid hormone (TH) and its activating enzyme, type 2 deiodinase, D2, in cancer progression, and found that TH is a critical regulator of Squamous Cell Carcinoma (SCC) tumorigenesis and that TH activation by D2 enhances the invasiveness of SCCs and their tendency to metastasize [15,16,17].