In an attempt to understand the role of the TGF-β - Smad - TMEPAI axis in promoting breast carcinogenesis, we studied relative contributions of Smad2 and Smad3 to the growth of breast cancer cells by altering endogenous Smad2 and Smad3 protein levels using shRNA as this approach mimics altered Smad3 to Smad2 ratios observed in cancer cells. This evidence concerns the gene SMAD3 and breast cancer.