NKX2-1 and cancer: When we compared the amount of GFP-positive A549 cells present in the lungs at an early timepoint (5 weeks) after cancer cell injection, we observed a twofold lower engraftment of NKX2–1 overexpressing cells in the lungs compared to empty vector control cells, indicating rather a tumour suppressive role of NKX2–1 (Fig. 6c).