Immunohistochemical and cytogenetic findings in malignant rhabdoid tumor

The histogenesis of malignant rhabdoid tumor (RT) remains a matter of controversy. From published reports it appears that some extrarenal RT (ERRT) exhibit neural or neuroectodermal features. Systematic investigation of renal RT (RRT) for neural differentiation has not yet been published. In this study, two RRT and two ERRT were investigated by light and electron microscopy, immunocytochemistry, and cytogenetic analysis.

All four cases exhibited similar morphology and a largely consistent immunohistochemical staining profile. Both tumor types showed immunoreactivity for various cytokeratins, epithelial membrane antigen (EMA), vimentin, neurofilaments, S100 protein, neuron specific enolase, Leu7, CD34, p53, MB2, MIC2, VS38c, laminin and fibronectin. Reactivity was usually confined to a small proportion of the tumor cells, especially in the case of antibodies against neurofilaments, NSE, S100 proteins Leu7, CD34 and p53. Only a few of the antibodies (anti-vimentin, MB2, MIC2, anti-EMA, and VS38c) stained the majority of the tumor cells. Chromosome analysis revealed a discrete aberration in 11p (most probably a paracentric inversion in 11p15) in the one RRT investigated. One ERRT had a normal karyotype, but the other one exhibited various structural abnormalities on chromosomes 18 and 22.

The immunohistochemical investigations revealed many similarities between RRT and ERRT, and all four tumors investigated exhibited neuroectodermal differentiation. As far as histogenetic classification is concerned, our findings point in the direction of the group of tumors that includes Ewing's sarcoma and primitive neuroectodermal tumors.