[Histology and prognosis of nephroblastoma--with special reference to special variants].

101 cases of Wilms' tumor (nephroblastoma) were investigated by light microscopy. In 80 cases a diagnosis of triphasic nephroblastoma was made. 21 cases were classified as special variants of Wilms' tumor. These included congenital mesoblastic nephroma (n = 5), fetal rhabdomyomatous nephroblastoma (n = 2), cystic partially differentiated nephroblastoma (n = 3), nephroblastoma with focal or diffuse anaplasia (n = 2), clear cell sarcoma or bone metastasizing renal tumor of childhood (n = 4), rhabdoid tumor (n = 2) and rhabdomyosarcomatous nephroblastoma (n = 3). Based on our own follow-up data and on information from the literature we propose to separate the group of nephroblastomas into three categories of different prognosis: 1. Nephroblastomas of low risk (congenital mesoblastic nephroma, fetal rhabdomyomatous nephroblastoma, cystic partially differentiated nephroblastoma) - in most of these cases simple nephrectomy sufficient as adequate therapy. 2. Nephroblastomas of standard risk (triphasic nephroblastomas) - therapy according to stage of disease. 3. Nephroblastomas of high risk (nephroblastomas with focal or diffuse anaplasia, clear cell sarcoma, rhabdoid tumor, rhabdomyosarcomatous nephroblastoma) - successful therapy has as yet to be developed.