ABCG2 and lung cancer: In addition, several of the upregulated genes, including ABCG2, BMP1/2, FGF1, IGF1, MYC, SOX1/2, WNT1 and NOTCH2, have been recently associated with cancer stem cells and tumour-initiating cells in lung cancer and other tumour types, as well as with epithelial-to-mesenchymal transition in tumours with poor prognosis (Fan et al, 2006; Moustakas and Heldin, 2007).