FN1 and breast cancer: To further assess the role of BST-2 in cell migration, we used a three-dimensional (3D) trans well assay (Figure 1C) in which the basal chamber of the trans well is filled with medium containing FBS and fibronectin (FN) to compare the effect of reduced BST-2 expression in the migration of four isogenic mouse breast cancer cell lines—4T1, 4T07, 168FARN, and 67NR.