Table 1 Children Oncology Group (COG) staging system for Wilms tumor

I

Tumor limited to kidney and completely resected with negative surgical margins. Renal capsule not involved. No tumor biopsy or rupture prior to removal. Renal vessels and hilar fat not involved.

II

Tumor extension beyond the kidney—to perinephric fat or to the vessels. Tumor resected completely with negative surgical margins.

III

Residual tumor after surgery:

 -Abdominopelvic lymph nodes involvement

 -Presence of tumor cells at the resection margins

 -Tumor biopsy or rupture before or during surgery

 -Tumor implants on the peritoneal surface

 -Irresectable tumor due to local vital organs involvement

IV

Hematogenous metastases or lymph node metastases outside the abdominopelvic region.

V

Bilateral renal involvement by tumor at the diagnosis.