Thyroid Differentiation Score (TDS), calculated using expression data of 16 thyroid-specific metabolic and functional genes12, showed that low TDS was associated with MTC tumors and high TDS with FTC tumors in dogs (Fig. 2A), except TC1088 which had very low TDS due to the loss of NKX2-1. Here, NKX2-1 is linked to thyroiditis.