Primary nephrectomy and intraoperative tumor spill: report from the Children's Oncology Group (COG) renal tumors committee.

Purpose: Initial Children's Oncology Group (COG) management for Wilms' tumor (WT) consists of primary nephroureterectomy with lymph node sampling. While this provides accurate staging to define further treatment, it may result in intraoperative spill (IOS), which is associated with higher recurrence rates and therefore requires more intensive therapy. The purpose of this study is to determine current rates and identify factors which may predispose a patient to IOS.