In vivo studies using a mouse model of heterotopic or orthotopic xenoengraftment of human NSCLC cells show that preferential sites of lung cancer metastases have significantly higher levels of CXCL12 protein expression than the primary tumor or plasma levels, suggesting that a chemotactic gradient may be established between the site of the primary tumor and metastatic sites [74]. The gene discussed is CXCL12; the disease is lung cancer.