[Show abstract][Hide abstract] ABSTRACT: Pleomorphic carcinoma (PC) of the lung consists of an epithelial component showing the histology of poorly differentiated non-small cell carcinoma of the lung and a sarcomatous component, that is more aggressive compared to non-small cell carcinoma of the lung. To determine the differences between an epithelial component of PC and poorly differentiated non-small cell carcinoma, the expression of adhesion molecules (E-cadherin, β-catenin and N-cadherin) and transforming growth factor-β (TGF-β) was compared immunohistochemically among 14 poorly differentiated adenocarcinomas of the lung (PDAs) and 14 PCs of the lung, with an epithelial component, showing the histology of PDA. Expression levels of E-cadherin and β-catenin were significantly lower in epithelial or sarcomatous components of PCs than in PDAs while that of TGF-β was significantly higher in epithelial components of PCs than in PDAs. No significant difference was found in incidences of the expression of these molecules between epithelial and sarcomatous components of PCs. No significant difference was noted in the expression level of N-cadherin among PDAs and epithelial and sarcomatous components of PCs. The present results showed that E-cadherin and β-catenin expression is reduced and TGF-β expression is increased in epithelial components of PCs with the same histology as PDA when compared to PDAs, suggesting that an epithelial component of PC is distinct from non-small cell carcinoma with the same histology.