NKX2-1 and neoplasm: Furthermore, among tumours with TTF‐1 protein expression, median OS was shorter in those patients whose tumours exhibited no expression of NKX2‐1/TTF‐1 exon 1 than in those patients with expression of NKX2‐1/TTF‐1 exon 1, although these differences were not significantly different; similar results were obtained among TTF‐1‐negative LADs, suggesting that a tumour suppressive role of NKX2‐1/TTF‐1 transcript isoforms lacking exon 1 may be independent of TTF‐1 protein expression (Figure 5E,F).