TTF1 and thyroid tumor: IHC analysis is helpful in distinguishing secondary thyroid neoplasms from primary thyroid tumors; for example, positive immunological staining of thyroglobulin and thyroid transcription factor-1 (TTF-1) indicates primary thyroid tumors, while secondary thyroid neoplasms usually do not express these markers but express specific markers related to their origin tissues [5,25,61,62,63].