To test these ideas, we compared the TGF-β1-arrested growth states of breast carcinoma cells and their presumed untransformed progenitors, the HMEC, and addressed the following issues: (i) Do Rac1 and Rac1b alter TGF-β1-induced cell migration and cell cycle arrest in breast carcinoma cells? The gene discussed is TGFB1; the disease is breast carcinoma.