CXCR4 and cancer: Among the 19 chemokine receptors, CXCR4 is the receptor most widely expressed by malignant tumors and whose role in tumor biology is most thoroughly studied.[18] The functional expression of CXCR4 induces lung cancer cell migration and adhesion to stromal cells when binding to its unique ligand stromal cell-derived factor-1 (SDF-1), which in turn provides growth- and drug-resistance signals to tumor cells.