IntroductionThymic epithelial tumours (TETs) are the relatively rare tumours originated from thymus. TETs are histologically categorised according to the WHO classification based on the morphology of epithelial tumour cells and proportion of lymphocytic involvement. Epithelio-mesenchymal transition (EMT) has reported to play pivotal roles in tumour progression including invasion/metastasis, drug resistance, and cancer stemness. However, the precise clinicopathological associations with EMT characteristics in TETs remain to be elusive. Herein, we have examined EMT markers in TETs integrated with their clinicopathological information.Material and methodsA total of 109 patients with TETs were surgically resected between 2002 and 2017 in our institution. Tissue samples were collected from the paraffine-embedded tumour blocks of these patients. The 2 mm cores in diameter of the most representative areas of the tumours were selected by the pathologist and assembled to make tissue microarrays. Immunohistochemical (IHC) stainings for E-cadherin (E) and vimentin (V) were performed. P63 and pan-cytokeratin were additionally stained to detect epithelial tumour cells. The expressions of these molecules were scored and quantified to categorise the activation level of EMT into three groups based on the combination of E and V levels: Full; E-V+, Partial; E+V+ or E-V-. Null; E+V-. For statistical analyses, chi-square tests and Cox hazard models were applied. P-value less than 0.05 was considered significant.Results and discussionsThe median follow-up time was 54.3 months (range, 0.3–178.7). Predominant WHO histological subtypes were as follows: A;8, AB;18, B1;30, B2;30, B3;6. C;15, others;2. Pathologic stage distributions by TNM classfication were as follows: 1;80, 2;2, 3;13, 4a;7, 4b;4. The positive rates of E-cadherin or vimentin expression in epithelial tumour cells were 54.2% and 57.9%, respectively. EMT activation was significantly exhibited in indolent predominant WHO subtype, and in the early stage of pT factor and the Masaoka classification (p=0.0005, 0.0493, and 0.0366, respectively). Multivariate analyses of overall survival time including pT, pN, pM, age, and EMT levels showed that pT factor was significantly prognostic (p=0.0218), but not for EMT.ConclusionEMT activation mechanisms in TETs were inversely correlated with their histological subtype and the primary tumour progression. Further studies are necessary to elucidate tumour progression mechanisms in TETs.