ABCG2 and cancer: Importantly, the GLI-1 gene was recently proposed to be involved in ABC transporter-independent oncological resistance, in which the TWIST1 and Snail gene transcription factors are linked to the Sonic Hedgehog pathway and induce tumor-initiating cancer stem-like cells, in both non-solid tumor-derived leukemia cells and solid-epithelial tumor-derived cervical cancer cells [25].