Adenomatoid tumor: immunohistological features suggesting a mesothelial origin.

Four adenomatoid tumors of the epididymis were evaluated immunohistologically for the expression of intermediate filaments and endothelial cell markers, factor VIII-related antigen and binding of Ulex europaeus I-lectin (UEA I). Immunofluorescence microscopy showed a strong reaction with antikeratin but not with anti-vimentin antibodies, indicating that adenomatoid tumor cells contain epithelial but not mesenchymal type of intermediate filaments. No staining of tumor cells was seen with anti-FVIII-related antigen antibodies or with fluorochrome-coupled UEA I. The results support the mesothelial, non-endothelial origin of adenomatoid tumors.