[Solid tumors in children. New advances and the importance of histological sub-classifications. I. Renal tumors in children].

New information is now provided to the pediatric pathologist through the application of new techniques as immunocytochemistry, cytogenetics, flow cytometry, etc... Their confrontation with better analysis of histopathology and extremely valuable data provided through Electron Microscopy and tissue culture has led to important progress in sub-classification of tumors, and especially definition of histologic patterns correlating with favorable or unfavorable response to therapy. This is especially true in the field of renal tumors. Clear cell sarcoma of the kidney (CCSK) and malignant rhabdoid tumors (MRTK) have recently been isolated as tumors of unfavorable prognosis. The actuarial 2-year survival rate is 49% for CCSK and 10% for MRTK (versus 95% for Wilms' Tumor). Amongst tumors of good prognosis are congenital mesoblastic nephroma which can be considered as a benign tumor, when no atypia is present, and cystic partially differentiated nephroblastoma, which is potentially malignant but in most cases is related to favorable outcome. Attention should be now focused on minimising the sequela of treatment, which requires different strategies according to extension of disease and histologic subclassification.