The most studied ABC family transporter protein subtype involved in drug efflux of HNSCC CSC is ABCG2, whereby its high expression correlates with marked chemoresistance and is mainly associated to the increase in canonical Wnt signaling pathway activity in HNSCC CSC (Zhang et al., 2009; Song et al., 2010; Yanamoto et al., 2011; Yao et al., 2013; Warrier et al., 2014). This evidence concerns the gene ABCG2 and head and neck squamous cell carcinoma.