Manipulation of expression of SDF-1 in breast cancer cells. (a) The efficiency of stromal cell-derived factor (SDF)-1 transfected in MDA-MB-231 cells was confirmed by PCR. M: marker; 1: negative control; 2: MDA-MB-231 wild-type; 3: empty vector control MDA-MB-231+/-; 4: SDF-1-transfected MDA-MB-231SDF1+/+. (b) Invasiveness of transfected cells. *P < 0.01 versus control and wild-type. (c) Cellular migration.