In agreement with these results, only the full-length and the ΔN-ter proteins reduced the speed of migration and RhoA activity (Fig. 9c,d) in shSCN4B cells, therefore demonstrating that the intracellular C-terminus of the SCN4B/β4 protein, and not the extracellular Ig-like domain, is needed to inhibit invasiveness in breast cancer cells. This evidence concerns the gene SCN4B and breast cancer.