(a) Invasion of MDA-MB-361/vIII and BT474/vIII cells was significantly stimulated by CXCL12 (50–100 ng/mL) (* = p<0.001; ANOVA). Cells were plated in 0.1% BSA/IMEM in the upper chamber of transwells with membranes with 8 µm pores, and with CXCL12 in the lower chamber. After 48 hours of incubation, the membranes were fixed and stained, and cells counted on the underside of the membranes. (b) The addition of a CXCR4 neutralizing antibody (10 µg/mL) and the small molecule inhibitor AMD3100 (10 µg/mL) significantly inhibited the invasion of cells towards CXCL12 (* = p<0.001, ANOVA). (c) The addition of only AMD3100 (10 µg/mL) significantly inhibited the basal invasive potential of MDA-MB-361/vIII cells (* = p<0.001, ANOVA). (d) The addition of Pertussis Toxin (P.T.) (0.25 µg/mL) significantly inhibited the overall invasion of cells toward serum (* = p<0.001, ANOVA). The results shown are the mean and SE from 10 fields counted on triplicate membranes, and is representative of repeated experiments.