Retrospective validation of a new staging system for Wilms' tumor.

Prognostic significance has been ascribed to certain clinicopathological features of the Wilms' tumor. Examples are size, vascular invasion, histologic characteristics, tumor rupture, and lymph nodal involvement. Several of these were arranged into a grouping system, and used in a cooperative clinical trial, the first National Wilms' Tumor Study (NWTS). Detailed clinicopathologic information was accumulated for each patient entered in the study, and these data were analyzed with respect to their prognostic import. Factors found to be of significance were rearranged into a proposed staging system, believed more likely to be predictive of outcome for patients with tumor spread beyond the kidney confines, but without distant metastases (Groups II and III). The postulated discriminatory superiority was tested using Group II and III patients entered in the second NWTS. The same children were reassigned retrospectively to Stages II and III, and the outcomes compared. Statistically significant differences were noted between Stages II and III, but not for Groups II and III. These results encourage the use of the new staging system in the third NWTS.