In addition to fundamental differences in the mechanism of Smad2 and Smad3 activation by TGF-β1, at least in PDAC cells, our study reveals that Rac1 may drive tumourigenesis in carcinoma cells with a still intact TGF-β/Smad pathway by favouring resistance to TGF-β1-mediated growth inhibition and by increasing TGF-β1-induced cell migration at the R-Smad epigenetic level. The gene discussed is SMAD3; the disease is carcinoma.