TTF-1 is a tissue-specific transcription factor expressed in the epithelial cells of thyroid and lung. This study investigates the immunohistochemical expression of TTF-I in pleural malignant mesotheliomas (MM) and adenocarcinomas (AC) of the lung, respectively. For this purpose, 33 biopsy specimens of pulmonary AC and 24 specimens of MM were studied, TTF-1 immunoreactivity was identified in 19 of 33 cases of AC (57.5%) and in none of the 24 cases of MM. Positivity for TTF-1 was 100% specific and 57.5% sensitive for lung AC, Alternatively, negativity for TTF-1 was 57.5% specific and 100% sensitive for MM. These results suggest that TTF-I can be favourably added to the immunohistochemical diagnostic panel for distinction between AC of the lung involving the pleura and pleural MM.
