We observed there might be a negative feedback loop between miR-206 (or miR-140) and TGF-β1 whereby these two miRNAs, downregulated by TGF-β1, participated in Smad3-dependent TGF-β1 signaling and negatively regulated TGF-β1/Smad3 signals in lung adenocarcinoma (Figure 8e). This evidence concerns the gene SMAD3 and lung adenocarcinoma.