CXCR4 and lung cancer: Lung cancer tissues from 105 patients who underwent complete tumor resection between January 1998 and June 2008 (sample group, 34 with brain metastasis during the follow-up period; control group 1, 34 without metastasis during the follow-up period; and control group 2, 37 with other organ metastasis, excluding brain metastasis, during the follow-up period) were examined by immunohistochemistry to detect the expression of CXCR4 protein.