Thymic Hodgkin's disease - A histological and immunohistochemical study ofthree cases

Thymic Hodgkin's disease (HD) shows some peculiar histological features dif ferent from nodal disease which are a result of the interaction with the sp ecific thymic microenvironment. We describe the histological and immunohist ochemical findings in three cases presenting as a primary thymic neoplasm b oth clinically and radiologically. Histological hallmarks were the prominen t formation of epithelium-lined cysts, inflammatory changes, a marked proli feration of thymic epithelium in association with Hodgkin- and Reed-Sternbe rg (RS) cells and the occurrence of the nodular sclerosing subtype in all c ases. The immunophenotype of the neoplastic cells was that of classical HD. They expressed CD30, CD15 and lacked CD45. In two cases CD20 expression wa s observed. All cases were negative for the latent membrane protein (LMP) o f the Epstein-Barr virus (EBV). The accompanying inflammatory infiltrate wa s rich in mature T-cells, but also showed a significant number of B-cells w ith frequent formation of follicles and proliferation of follicular dendrit ic cells. Thymic HD develops in a microenvironment with features of thymic medulla as defined by the morphology and pattern of the proliferating epith elial cells and the mature immunophenotype of the admired thymocytes. These findings, especially the CD20 positivity in Hodgkin and RS-cells, may poin t to the possible origin of thymic HD from medullary B-cells.