BackgroundThe epithelial–mesenchymal transition (EMT) describes the process through which cells lose epithelial characteristics and gain a mesenchymal phenotype. The EMT contributes to tumor invasion and cancer progression, and is associated with metastasis and poor survival of patients with non–small-cell lung cancer. However, little is known about the relationships between the EMT and the clinicopathologic characteristics of patients with stage IA lung adenocarcinoma. Patients and MethodsWe conducted immunohistochemical analysis of the expression of the EMT markers E-cadherin and vimentin of specimens acquired from 183 consecutive patients with stage IA lung adenocarcinoma. The clinicopathologic significance of the association of the EMT status with E-cadherin and vimentin expression was analyzed after propensity score matching. ResultsE-cadherin and vimentin were detected in 68.3% and 18.6% of stage IA lung adenocarcinomas, respectively. The presence of cells with EMT conversion was associated with older patient age. A propensity score–matched cohort (128 patients) was used for further analyses. Computed tomography revealed that tumors with EMT conversion showed solid-dominant nodules compared to those without conversion. Survival analysis after propensity score matching showed that the EMT correlated with poor disease-free survival (hazard ratio = 2.57, P = .0451) and overall survival (hazard ratio = 4.23, P = .0471). Multivariate analysis revealed that the EMT was an independent predictor of shorter disease-free survival. ConclusionThe EMT was a significant predictor of poor prognosis of patients with stage IA lung adenocarcinoma. The EMT status may serve as an indicator for administering adjuvant therapy.