ABCG2 and non-small cell lung carcinoma: It has also been found that the hedgehog (Hh) signaling pathway is inappropriately activated in EGFR TKI resistant NSCLC cells, though silenced in EGFR TKI sensitive cells, implicating Hh activation in the development of EGFR TKI resistance via the induction of EMT and upregulation of the stem cell marker ABCG2 (Figure 2) [66].