Thyroid TranscriptionFactor-1 (TTF-1)

TTF-1 is a 40kDa thyroid transcription factor expressed in thyroid and lung epithelial cells. TTF-1 was expressed in most small cell lung carcinomas, lung adenocarcinomas, undifferentiated large cell lung carcinomas, atypical carcinoids and few typical carcinoids, but not in lung squamous cell carcinomas. The expression of TTF-1 was also positive in papillary thyroid carcinoma, but negative in other tissues. Therefore, TTF-1 can be used to identify lung adenocarcinoma and squamous cell carcinoma, together with lung adenocarcinoma metastases to extrapulmonary sites.