TGFB1 and squamous cell carcinoma: Numerous recent studies have demonstrated multiple signaling pathways, such as the TGF-β and Wnt/β-catenin pathways, are required for self-renewal and maintenance of the CSC phenotype.36, 37, 38 Activation of the TGF-β pathway has been reported to contribute to tumor heterogeneity and chemoresistance in squamous cell carcinoma CSCs, leading to tumor recurrence.23 Inhibition of the TGF-β pathway decreases the CD44high/Id1high glioma-initiating cell population and reduces the capacity of glioma-initiating cells to initiate tumors,39, 40 suggesting TGF-β is a key regulator of CSCs.