CXCR4, the ligand of stromal cell-derived factor 1a/chemokine (C-X-Cmotif) 12, is an important molecule involved in the spreading and progression of tumor (Zlotnik, 2008). Our previous work has shown that CXCR4-positive circulating tumor ASP3026
(CTCs) exist in the blood of solid tumor patients (Fusi et al., 2012). We recently found that CXCR4-positive CTCs are more stem-like than other type of CTCs in NSCLC patients (Yin et al., 2015). Moreover, CXCR4 promotes EMT by activation of the Wnt/?-catenin signaling pathway in colorectal cancer (Hu et al.,
2014), and there is a crosstalk existed among the TGF-? and CXCR4 pathways in liver tumor (Bertran et al., 2013). These studies suggest CXCR4 plays an important role in EMT and CSCs. In this study, we perform EMT RT2 Profier PCR Array to screen the EMT markers in CXCR4-positive subpopulation of gefitinib-resistant A549 cell line, because the up-regulation of CXCR4 is functionally crucial for maintenance of stemness in drug-resistant NSCLC cells
(Jung et al., 2013).