A qRT-PCR analysis also showed that expression of TGFBR2 and SMAD3 was decreased in SCLC cells, but other TGF-β signaling components, including SMAD2, SMAD4 and TGFBR1 (the gene that encodes TβRI), were expressed at normal levels in these cells (Figure 1c). Here, TGFB1 is linked to small cell lung carcinoma.