NKX2-1 and lung adenocarcinoma: Surfactant apoproteins, including surfactant protein-A (Sp-A) and surfactant protein-B (Sp-B) are used as markers for lung adenocarcinoma and thyroid transcription factor-1 (TTF-1) is used as a marker for lung adenocarcinoma, large cell carcinoma, small cell carcinoma and thyroid carcinoma (Kaufmann and Dietel, 2000b).