In thyroid tumor, there appears to be a progressive decrease of TTF-1 nuclear staining from follicular adenoma to well-differentiated carcinoma, then to anaplastic carcinoma, consistent with the progressive dedifferentiation and increasing malignancy of thyroid tumors (16) The loss of TTF-1 and Pax8 (thyroid-specific transcription factor) correlated with the aggressiveness of thyroid carcinoma and their overexpression induced differentiation of anaplastic thyroid carcinoma (16–18). This evidence concerns the gene TTF1 and thyroid gland undifferentiated (anaplastic) carcinoma.