PAX8 and thyroid gland undifferentiated (anaplastic) carcinoma: In the latest World Health Organization classification of endocrine and neuroendocrine tumors, primary thyroid squamous cell carcinoma is included in anaplastic thyroid carcinoma,because squamous cell carcinoma of the thyroid often displays BRAF p.V600E mutations (87%) and exhibits positive immunohistochemical staining for the follicular cell markers PAX8 (91%) and TTF1 (38%) (6).