Malignant rhabdoid tumor. A morphological and flow cytometric study.

Sixteen cases of malignant rhabdoid tumor (MRT) were studied by conventional light microscopy, immunohistochemistry, electron microscopy and flow cytometry. The age of the 16 patients varied from two months to 25.9 years. There were 11 males and five females. Eleven tumors were located in the kidney. The remaining five were found in the chest wall (n = 2) and the head and neck (n = 3). Particular histopathological findings included myxoid, pseudoalveolar and hyalinized areas. By immunohistochemistry, 15/15 cases stained positively for vimentin, 9/14 for cytokeratin, 6/15 for desmin, 9/14 for epithelial membrane antigen (EMA), 10/14 for neuron specific enolase (NSE) and 10/15 for protein S-100. Stains for neurofilaments, myoglobin and Ulex europaeus aggl. I (UEA I) were negative. The characteristic finding by electron microscopy in three cases were large numbers of intermediate filaments arranged either randomly or in concentric whorls. None of the 11 cases studied revealed aneuploid DNA stem lines as determined by flow cytometry. Of the 16 patients 12 died, one is living with disease and three are living without evidence of disease. Postoperative treatment consisted of chemotherapy, in some cases combined with radiotherapy. Two patients developed a medulloblastoma in addition to a renal and extrarenal MRT, respectively. Our findings demonstrate that MRT may present more histopathological patterns than hitherto recognized. In addition, they show that MRT may express a wide range of antigenic "markers", similar to epithelioid sarcoma with which it may be confused on cytological grounds. Despite aggressive postoperative chemotherapy prognosis is still poor.