In vitro studies confirmed that halofuginone inhibited TGF-β signaling in breast and prostate cancer cells as shown by: a) reduction of TGF-β receptor II protein, b) inhibition of Smad intracellular mediators, c) inhibition of a TGF-β-responsive reporter and d) reduction of prometastatic TGF-β-regulated genes. This evidence concerns the gene TGFB1 and prostate carcinoma.