SUMMARY Childhood renal tumors account for ~7% of all childhood cancers, and most cases are embryonic Wilms’ tumors (WT). Children with WT are usually treated by either COG or SIOP. The later treats the children using preoperative chemotherapy, but both have around 90% of overall survival in five years. WT is a genetically heterogeneous group with a low prevalence of known somatic alterations. Only around 30% of the cases present mutation in known genes, and there is a relatively high degree of intra-tumor genetic heterogeneity (ITGH). Besides potentially having an impact on the clinical outcome of patients, ITGH may interfere with the search for molecular markers that are prospectively being tested by COG and SIOP. In this review, we present the proposal of the current UMBRELLA SIOP Study 2017/Brazilian Renal Tumor Group that requires the multi-sampling collection of each tumor to better evaluate possible molecular markers, as well as to understand WT biology