Abstract: Objective To identify the expression of thyroid transcription factor 1（TTF-1）in the squamous cell carcinoma of lung，and to explore its diagnostic value in classification of lung cancer. Methods TTF-1 from 140 biopsy specimens of lung were detected with S-P staining of immunohistochemistry，and their clinical data were analyzed and relevant literatures were reviewed. Results In this study，27 specimens of lung adenocarcinomas have showed positivity for TTF-1，and TTF-1 was not expressed in 54 specimens of squamous cell carcinoma of lung，the difference was statistically significant（P < 0. 01）；in addition，the positive rate of TTF-1 was up to 95% in small cell lung carcinoma. Conclusion TTF-1 is not expressed in the squamous cell carcinoma of lung and has high expression in the lung adenocarcinomas. The correct determination of TTF- 1 contributes to correct classification of lung cancer.

Key words: TTF-1, squamous cell carcinoma of lung, lung adenocarcinomas, immunohistochemistry