TTF1 and lung carcinoma: TTF-1 is a thyroid transcription factor involved in the development of the embryonic thyroid, which is coded by NKX2-1, which shows diffuse strong positive expression in thyroid cancer and lung cancer.[33–35] Oishi et al[35] suggested 3 mechanisms to explain the abnormal TTF-1 expression in TL-LGNPPA: TL-LGNPPA may originate from ectopic thyroid tissue.