To better characterize the biological functions of TGF-β signaling in Clara cells in the development of lung cancer, we subjected the CC10-Smad7 transgenic mouse with urethane treatment to induce lung cancer and investigated how TGF-β signaling in Clara cells might contribute to the development of lung cancer, in addition to its effect in the development of allergic asthma. This evidence concerns the gene TGFB1 and allergic asthma.