Malignant renal rhabdoid tumour. Immunohistochemical and ultrastructural studies.

In an effort to establish their possible histogenesis, three cases of renal rhabdoid tumour and their metastases were studied both by a battery of polyclonal and monoclonal antibodies using the avidin-biotin-peroxidase complex technique and by electron microscopy. Vimentin was demonstrated in renal rhabdoid tumour in two cases and in all metastatic deposits. Cytokeratin (39, 43 and 50 kD) was not demonstrable in the three renal rhabdoid tumours, but was strongly positive in all metastatic lesions in one case. Epithelial membrane antigen was present in one renal rhabdoid tumour and in pulmonary metastases in two cases. Ultrastructural study showed epithelial differentiation in all tumours: basal lamina and convergent tight junctions were demonstrated; intracytoplasmic intermediate filaments were present in all primary and metastatic tumours. Rhabdoid tumours thus exhibited heterogeneous immunophenotypic expression suggesting that they are derived from mesenchymal cells which are capable of differentiating into epithelial cells.