TTF1 and head and neck neoplasm: The 4th edition of the World Health Organization Classification of Head and Neck Tumors (WHO-HNT) indicates that NPPA with positive expression of cytokeratin 19 (CK19) and TTF-1 and negative expression of TG is called TL-LGNPPA.[38] In summary, TL-LGNPPA and PTC were positive for TTF-1 and CK19.