TGFB1 and small cell lung carcinoma: SOX4 is a known target gene of the TGF-β signaling pathway, via the direct binding of SMAD2/3 in complex with SMAD4 to the SOX4 gene promoter region, and has been shown to be related to the regulation of neural-related nature target genes in SCLC lung tumors with neuroendocrine characteristics (Castillo et al., 2012).