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. The gene discussed is SMAD7; the disease is lung carcinoma.