Pathological evaluation of renal tumors in children: international society of pediatric oncology approach.

In the majority of European countries, children with renal tumors now enter the SIOP-93-01 Trial and Study. The objective of this Study is to refine methods of treatment especially in stage I patients. The role of institutional pathologists is important in this trial. There are new criteria for stages I and II, a new SIOP Working Classification of Renal Tumors of Childhood, and morphologic and prognostic similarities of pretreated and non-pretreated anaplastic cases. Specific problems encountered in assessing tumors treated with preoperative chemotherapy, administered to the majority of children over 6 months of age entering the SIOP Study, are discussed. The identification of a new low-risk group, the completely necrotic Wilms tumor, is outlined.