NKX2-1 and lung adenocarcinoma: NK2 homeobox 1, also known as thyroid TF-1 (TTF-1), was demonstrated to be frequently suppressed in high-grade lung adenocarcinoma.26 The tumors formed by A549-WT cells were TTF1-negative, whereas TTF1-positive cells were observed in tumors formed by A549-GAC (S314A) cells (Fig. 6i).