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Wilms Tumor



Classification of Renal tumors


The childhood kidney tumor pathology classification system is used by the Children's Oncology Group (COG) to stratify the different renal tumors depending on pathology, prognosis and risk of relapse.

Treatment of pediatric renal tumors is determined on the basis of histopathological
classification and surgical stage.

This entire website section deals with Wilms tumor as it is by far the most common renal tumor in children. However, the COG organized clinical studies where treatment given for any childhood renal tumor depended on the pathological subtype.  In this way, as well as gaining more knowledge about Wilms tumor, unusual tumors which generally have a worse prognosis could be included in clinical studies.


Pathological Type of Renal Tumor Characteristics Risk Group
Mesoblastic Nephroma
  • Most common tumor of kidney in first month of life
  • Median age at presentation is 3 months
  • No malignant epithelial component
  • Treated by surgery alone
Very low risk
Nodular Renal Blastemas and Nephrogenic Rests
  • Pre-Wilms tumor
Very low risk
Wilms tumor Favourable Histology (FH)
  • Triphasic embryonal neoplasm (see pathology section)
Low or high risk Wilms tumor depending on Stage


Histology (UH)

  • 7.5% of all pediatric renal tumors
  • Triphasic embryonal neoplasm (see pathology section)
  • Diffuse anaplasia present (see pathology)
Very high risk renal tumor
Rhabdoid tumor of kidney (RTK)
  • 1.6% of all pediatric renal tumors
  • Highly malignant tumor
  • Uniform rhabdomyoblastic cellular infiltrates
  • Common in first two years of life
  • Associated with bone and CNS metastases
  • Poor prognosis
Very high risk renal tumor
Clear Cell Sarcoma of the kidney (CCSK)
  • 3.5% of all pediatric renal tumors
  • Primitive mesenchymal neoplasm
  • 4% of childhood renal tumors
  • Survival improved with RT and Adriamycin, but poor prognosis
Very high risk renal tumor
Renal cell carcinoma Very high risk renal tumor


There is an ongoing Children's Oncology Group renal tumor biology study AREN03B2

The goal of this study is to improve the current classification schema to better stratify patients into risk-appropriate treatment groups. This study will serve to identify prognostic markers (histopathology, disease stage, chromosome 1p and 16q allelic status (LOH) and response evaluation (diagnostic pulmonary imaging). These data are required for registration and stratification of all renal tumors entered on therapeutic trials. A reference bank containing genetically characterized histopathologic slides, frozen tumor tissue, tumor DNA, paired normal DNA, patient serum and urine will be maintained. The bank will also collect outcome data on patients not enrolled on a subsequent therapeutic trial. This bank will help investigators to facilitate future research including the
analysis of novel prognostic markers.




Cellular classification of renal tumors at the National Cancer Institute


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