E-CADHERIN EXPRESSION IN THYMOMAS

For the purpose of investigating the pattern of E-cadherin (E-CD) expr ession in thymomas, 72 cases were immunostained using monoclonal antib ody (HECD-1) and microwave-enhanced immunohistochemical method on form alin-fixed, paraffin-embedded tissue sections. The thymomas were class ified according to modified Muller-Hermelink classification. The spind le-shaped, medullary type tumor epithelial cells in medullary (3 cases ) and composite type (20 cases) thymonas rarely expressed E-CD except in focal areas showing microcystic change observed in 8 cares. Meanwhi le, the cohesive epithelioid tumor cells in every case of well-differe ntiated thymic carcinomas (WDTC) (29 cases) expressed E-CD. The epithe lial cells in cortical type (13 cases) expressed stronger E-CD compare d with those of organoid type (7 cases). In cases of WDTC admired with cortical type, we observed increasing expression of E-CD as the tumor epithelium forms cohesive sheets. We could not find any loss of E-CD expression in invasive foci of the 11 cases of high-staged WDTC examin ed. Since the results of our study show a strong correlation between E -CD expression and epithelioid morphology of the tumor, E-CD seems to play a major role as a morpho-regulatory factor rather than as a suppr essor of invasion in organotypic thymomas.