To determine whether Rac interacts with proteins in the AKT/mTOR and MEK/ERK signaling cascades in breast cancer cells, we performed Rac pulldown assays: beads coated with protein encoding the p21-binding domain (PBD) of the Rac/CDC42 effector PAK1 are used to capture active GTP-bound Rac and CDC42, which are then detected by immunoblot analysis of bead eluates. Here, CDC42 is linked to breast carcinoma.