In this study, we found that in breast cancer cells, FilGAP localizes to invadopodia through its pleckstrin-homology (PH) domain binding to phosphatidylinositol 3,4-bisphosphate [PI(3,4)P2] on membranes and down-regulates invadopodia formation by inactivating Rac1. Here, RAC1 is linked to breast carcinoma.