The effect of preoperative therapy on the histologic features of Wilms' tumor. An analysis of cases from the Third National Wilms' Tumor Study.

Preoperative chemotherapy is being used with increasing frequency in the US for the management of selected children with Wilms' tumor, despite relatively limited knowledge as to the effects of such therapy on tumor histologic features. The authors reviewed pathologic material from all preoperatively treated unilateral Wilms' tumors registered on the third National Wilms' Tumor Study. Preoperative therapy was associated with increased ambiguity of tumor stage. The prevalence of anaplasia in the 83 evaluable specimens was similar to, although slightly increased over, that in comparable high-stage untreated Wilms' tumors (11% versus 5% to 8%), and it appeared to retain its adverse connotations. These data also suggest that alterations of tumor character and distribution by therapy provide useful prognostic information. All 17 children whose residual viable tumor was limited to intrarenal sites at the time of resection were alive and disease-free at last follow-up. Extensive (greater than 90%) tumor necrosis, low mitotic activity, and high degrees of differentiation of residual tumor were also associated with favorable outcomes. Although careful utilization of preoperative chemotherapy can be of value in children with otherwise difficult-to-manage Wilms' tumors, the potential benefits of preoperative tumor bulk reduction must be weighed against the risk of overtreatment or undertreatment as a result of increased ambiguity of tumor stage.