According to the results of exfoliative cytology of drainage fluid and immunohistochemistry [CK (AE1/AE3) (+), CK56 (−), CD68 (−), CD45 (LCA) (−), TTF-1 (+), p40 (+), D2-40 (−), and ki-67 (50%+)], adenocarcinoma of lung origin was considered (Fig. 2A–F). The gene discussed is TTF1; the disease is adenocarcinoma.