In this study, the salient features are (1) to our knowledge, this is the first study, to determine the role of miR-20a in suppressing antitumor effects of TGF-Δ in NSCLC through downregulation of TβRII by binding to its 3′-UTR; (2) to study the mechanism of how c-Myc is involved in the regulation of TβRII through the regulation of miR-20a expression; and (3) to investigate how the loss of miR-145 in lung cancer cells can demote TGF-β signaling through regulating miR-20a and TβRII expression. Here, MYC is linked to lung cancer.