Since TGF-β signal is transduced even in the low expression levels of Smad3 if Smad2 is expressed in H146 cells (Figure 1b), we assumed that TGF-β signal transduction was attenuated in SCLC cells through the decreased expression of TβRII, and therefore, we decided to focus on the roles of TβRII in SCLC in the present study. The gene discussed is SMAD3; the disease is small cell lung carcinoma.