CXCR4 and lung cancer: Because lung cancer cells express CXCR4 (CD184), and stromal cells within the tumor microenvironment constitutively secrete SDF-1, which is the ligand for CXCR4 [26], we asked whether activation of the CXCR4/SDF-1 axis could be involved in migration to the metastatic site and drug resistance in our model.