SMAD2 and small cell lung carcinoma: In the current study, we observed that fifteen EMT genes were differentially expressed among the PNENs, including (MMP3, ITGAV, KRT14, PLEK2, SNAI2, GSK3B, ITGB1, MAP1B, TCF3, VPSA13, SMAD2, MMP2, SPARC, WNT5A, and ITGA5), among which three genes were also selected in our previous study allowing for the discrimination of TC from AC (SNAI2), LCNEC from AC (KRT14, PLEK2, and SNAI2), and SCLC from AC (PLEK2 and SNAI2).