[Malignant rhabdoid tumor of the kidney: 2 cases and a review of the literature].

Report of the microscopic, ultrastructural and immunohistochemical findings of two malignant rhabdoid tumors of the kidney in two males aged 2 1/2 and 19 months. The incidence of this tumor in our files is 1.9% of all the renal tumors of infancy. Both cases were formally considered to be rhabdomyosarcomatous variants of nephroblastomas. Microscopically a slightly cohesive polygonal cell proliferation is shown. The cells have intracytoplasmatic hyaline inclusions ultrastructurally identifiable as intermediate filament bundles, showing positivity to vimentin in the immunohistochemical technique. Malignant rhabdoid tumors are referred to as very aggressive tumors with a poor response to treatment and a high mortality rate. Association with central nervous tumors and hypercalcemia has been reported. The clinical and pathologic features make it possible to differentiate them from nephroblastomas, although the histogenesis is not definitely established.