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Wilms Tumor





The staging system used in the National Wilms Tumor Study (NWTS) is the accepted staging system.

The staging system is based on imaging and surgery.


Staging system used in National Wilms Tumor Study 3 and 4:


Tumor limited to kidney and completely excised

  1. Surface of renal capsule is intact
  2. Tumor was not ruptured before or during removal
  3. No residual tumor apparent beyond the margins of resection


Tumor extends beyond the kidney but is completely removed
1 or more of the following features must be present:

  1. Tumor extends beyond the kidney but is completely excised
  2. No residual tumor is apparent at or beyond the margins of excision

Any of the following conditions may also exist:

  1. Tumor involvement of the blood vessels of the renal sinus and/or outside the renal parenchyma

Other features:

  1. Regional extension of the tumor- penetration through the outer surface of the renal capsule into the perirenal soft tissue
  2. Vessels outside the kidney substance are infiltrated or contain tumor thrombus
  3. No residual tumor apparent at or beyond the margins of excision


>1 of the following criteria must be met:

  1. Unresectable primary tumor
  2. Lymph node metastasis
  3. Positive surgical margins
  4. Tumor spillage involving peritoneal surfaces either before or during surgery, or transected tumor thrombus.  This includes: The tumor has been biopsied prior to removal or there is local spillage of tumor during surgery, confined to the flank

Residual non hematogenous tumor confined to abdomen. Any one or more of the following occur:

  1. Lymph nodes on biopsy are found to be involved in the hilus, the periaortic chains, or beyond
  2. The tumor has been biopsied prior to removal or there is local spillage of tumor during surgery, confined to the flank
  3. There has been peritoneal contamination by tumor such as by spillage of tumor beyond the flank before or during surgery, or by tumor growth that has penetrated through the peritoneal surface
  4. Implants are found on the peritoneal surfaces
  5. The tumor extends beyond the surgical margins either microscopically or grossly
  6. The tumor is not completely resectable because of local infiltration into vital structures


Hematogenous metastases

  1. Deposits beyond stage III (eg. lung, liver, bone, and brain)


Bilateral renal involvement at diagnosis: an attempt should be made to stage each side according to the above criteria on the basis of extent of disease before biopsy

  1. Staging, which is the same for tumors with favorable and with unfavorable histologic features
  2. Tumors of unfavorable type are those with focal or diffuse anaplasia, or those with sarcomatous histology


Staging and Prognosis:

Prognosis is determined in part by favorable or unfavorable histology. Patients with favorable histology tumors have at least an 80% overall survival rate at 4 years after initial diagnosis. This is even true for patients with stage IV disease. Overall survival for unfavourable histology is only about 20 - 30%.


Frequency of Different Stages at Diagnosis:

Difficulties of Staging

  • The renal capsule can become obscured by reactive fibrosis in the perirenal fat. Extension of the tumor beyond the renal capsule can be difficult, or even impossible, to determine.
  • The renal sinus is often infiltrated. Vessels in this region probably represent the earliest manifestation of extrarenal spread in the majority of cases.
  • There are often difficulties in distinguishing stage I and stage II disease. NWTS traditionally distinguishes stage I from stage II involvement of the renal sinus on the basis of whether or not tumor has invaded beyond the medial margin of the renal outline, the hilar plane. This criterion has been proven unsatisfactory. The position of the hilar plane is almost always in part distorted by tumor.


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