LUNG CANCER

Thyroid transcription factor 1 (TTF-1) is an impor-tant transcription factor in lung morphogenesis and regulates gene expression of type 2 pneumocytes and Clara cells in the postnatal lung. 1 It is an impor-tant marker in the immunohistochemistry (IHC) panel for the diagnosis of pulmonary adenocarci-noma. 2,3 TTF-1-positive lung adenocarcinoma was found to have a morphologic resemblance to type 2 pneumocytes, Clara cells, and nonciliated bronchiolar cells. 4 Previous studies showed that TTF-1 expression is a signifi cant prognostic factor of better survival in lung adenocarcinoma. 5-8 Furthermore, epidermal growth factor receptor (EGFR) mutation is associated with TTF-1 expression in lung adenocarcinoma. 9,10 TTF-1-positive adenocarcinoma also shows a higher prevalence of negative p53 staining, less frequen