NKX2-1 and neoplasm: As such, at early-disease stage, NKX2–1 overexpression might limit ROS levels needed to acquire additional oncogenic driver mutations and in this way function as a tumour suppressor, which could explain our observation that NKX2–1 overexpressing A549 cells engrafted to a lesser extent in the lungs at early-disease stage (Fig. 6c).