[Nephroblastomas (Wilms' tumors) and special variations of nephroblastomas].

The results of the National Wilms' Tumor Study (NWTS) enabled the subdivision of nephroblastomas into subtypes with "favorable and unfavorable histology". Nephroblastomas with "unfavorable histology" could be discriminated by identifying those tumors not responding to therapeutic regimes proven successful for most cases with "favorable histology". A major disadvantage of the NWTS classification has been the exclusion of cytodifferentiated nephroblastoma variants, which, in contrast to typical nephroblastomas, can be cured by complete nephrectomy with wide excision of perinephric soft tissue. In the current study all types of nephroblastoma and nephroblastoma variants were included to encompass the whole morphological spectrum which these tumors may assume. This unselected material is necessary to define the relation between morphology and prognosis and to compare the treatment results of various clinical trials. Three hundred and four cases of nephroblastoma and related neoplasms on file at the Pediatric Tumor Registry, Kiel, were investigated by conventional light microscopy, electron microscopy, immunohistochemistry and DNA-flow cytometry. Of the "typical" nephroblastomas 50% occurred in the left kidney, 45% in the right kidney, and 5% were bilateral. Five cases were located in extrarenal sites. There were 121 males and 114 females. The peak incidence was noted in the third year of life. Of 135 patients 111 are alive and well, nine are living with disease, and 10 patients have died of disease. The blastemal predominant and stromal predominant types in our study were more frequent than in the NWTS. By contrast, the mixed and epithelial predominant types were more frequent in the NWTS. Patients with nephroblastomas of mixed or blastemal predominant type were older than those with epithelial predominant or stromal predominant type. Electron microscopy showed that nephroblastoma is derived from metanephric blastema. Blastemal cells are capable of differentiating into tubular epithelial cells and stromal cells. Undifferentiated blastemal cells contain exclusively vimentin intermediate filaments, better differentiated blastemal cells vimentin and cytokeratin, and stromal cells exclusively vimentin. Preoperative radio- and/or chemotherapy led to a marked reduction of undifferentiated blastema and poorly differentiated tubules, whereas better differentiated tubules, striated muscle, hyaline cartilage, cells with anaplastic and sarcomatous elements were not affected. Thus, identification of highly malignant nephroblastomas with anaplasia and sarcomatous renal tumors was even possible after preoperative treatment. Congenital mesoblastic nephroma (CMN; n = 17) is a low-grade malignant, cytodifferentiated nephroblastoma which very rarely occurs beyond the fourth month of life and has an excellent prognosis, provided it has been completely resected.(ABSTRACT TRUNCATED AT 400 WORDS)