ABCB1 and neoplasm: Similar to tumor cells and epithelial cells, ABCB1 expression (mRNA and protein) in CSCs is largely governed by transcriptional regulation, which has been demonstrated for Kelch-like ECH-associated protein 1 (KEAP) with nuclear factor erythroid 2-related factor 2 (NRF2)[110], OCT-4/POU5F1[67,111], NANOG/STAT3[112], Twist[113], and Wnt/β-catenin[114].