Wilms Tumor

Wilms Tumor - What is Wilms Tumor?

Wilms tumor or nephroblastoma is cancer of the kidneys that typically occurs in children, rarely in adults.

Its common name is an eponym, referring to Dr. Max Wilms, the German surgeon (1867–1918) who first described this kind of tumor.

Approximately 500 cases are diagnosed in the U.S. annually. The majority (75%) occur in otherwise normal children; a minority (25%) is associated with other developmental abnormalities. 

People of African descent have the highest rates of Wilms' tumor. Females are also more likely than males to develop the tumors. Most instances of cancer occur among children under the age of 5.

It is highly responsive to treatment, with about 90% of patients surviving at least five years.

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Wilms Tumor Pathology

Most nephroblastomas are unilateral, being bilateral in less than 5% of cases. They tend to be encapsulated and vacularized tumors that do not cross the midline of the abdomen. In cases of metastasis it is usually to the lung. A rupture of Wilms tumor put the patient at risk of hemorrhage and peritoneal dissemination of the tumor. In such cases, surgical intervention by a surgeon who is experienced in the removal of such a fragile tumor is imperative.

Pathologically, a triphasic nephroblastoma comprises three elements:

  • blastema
  • mesenchyme
  • epithelium

Wilms' tumor is a malignant tumor containing metanephric blastema, stromal and epithelial derivatives. Characteristic is the presence of abortive tubules and glomeruli surrounded by a spindled cell stroma. The stroma may include striated muscle, cartilage, bone, fat tissue, fibrous tissue. The tumor is compressing the normal kidney parenchyma.

The mesenchymal component may include cells showing rhabdomyoid differentiation. The rhabdomyoid component may itself show features of malignancy (rhabdomyosarcomatous Wilms).

Wilms' tumors may be separated into 2 prognostic groups based on pathologic characteristics:

  • ''Favorable'' - Contains well developed components mentioned above
  • ''Anaplastic'' - Contains diffuse anaplasia (poorly developed cells)

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Wilms' Tumor Prognosis

Tumor-specific loss-of-heterozygosity (LOH) for chromosomes 1p and 16q identifies a subset of Wilms tumor patients who have a significantly increased risk of relapse and death.

LOH for these chromosomal regions can now be used as an independent prognostic factor together with disease stage to target intensity of treatment to risk of treatment failure.

Genome-wide copy number and LOH status can be assessed with virtual karyotyping of tumor cells (fresh or paraffin-embedded).

The overall prognosis with surgical removal is positive.

Early removal tends to promote positive outcomes.

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Wilms Tumor Treatments

Once a kidney tumor is found, a surgical biopsy is done. A sample of tissue from the tumor is sent to a pathologist, who looks at it under a microscope to check for signs of cancer.

If the tumor is only in the kidney (typical), it can be removed along with the whole kidney (a nephrectomy).

If there are tumors in both kidneys or if the tumor has spread outside the kidney, a piece of the tumor will be removed.

Children 16 years old or older have higher mortality rates within their stages. This is due to them being treated less aggressively and consistently.

Adjuvant chemotherapy is sometimes used.

Staging is determined by combination of imaging studies and pathology findings if the tumor is operable. Treatment strategy is determined by the stage:

Stage I (43% of patients)

For stage I Wilms' tumor, 1 or more of the following criteria must be met:

  • Tumor is limited to the kidney and is completely excised.
  • The surface of the renal capsule is intact.
  • The tumor is not ruptured or biopsied (open or needle) prior to removal.
  • No involvement of renal sinus vessels.
  • No residual tumor apparent beyond the margins of excision.

Treatment: Nephrectomy +/- 18 weeks of chemotherapy depending on age of patient and weight of tumor. EG: less than 2 years old and less than 550g only requires Nephrectomy with observation

Outcome: 98% 4-year survival; 85% 4-year survival if anaplastic

Stage II (23% of patients)

For Stage II Wilms' tumor, 1 or more of the following criteria must be met:

  • Tumor extends beyond the kidney but is completely excised.
  • No residual tumor apparent at or beyond the margins of excision.
  • Any of the following conditions may also exist:
    • Tumor involvement of the blood vessels of the renal sinus and/or outside the renal parenchyma.
    • The tumor has been biopsied prior to removal or there is local spillage of tumor during surgery, confined to the flank.

Treatment: Nephrectomy + abdominal radiation + 24 weeks of chemotherapy

Outcome: 96% 4-year survival; 70% 4-year survival if anaplastic

Stage III (23% of patients)

For Stage III Wilms' tumor, 1 or more of the following criteria must be met:

  • Unresectable primary tumor.
  • Lymph node metastasis.
  • Positive surgical margins.
  • Tumor spillage involving peritoneal surfaces either before or during surgery, or transected tumor thrombus.

Treatment: Abdominal radiation + 24 weeks of chemotherapy + nephrectomy after tumor shrinkage

Outcome: 95% 4-year survival; 56% 4-year survival if anaplastic

Stage IV (10% of patients)

Stage IV Wilms' tumor is defined as the presence of hematogenous metastases (lung, liver, bone, or brain), or lymph node metastases outside the abdomenopelvic region.

Treatment: Nephrectomy + abdominal radiation + 24 weeks of chemotherapy + radiation of metastatic site as appropriate

Outcome: 90% 4-year survival; 17% 4-year survival if anaplastic

Stage V (5% of patients)

Stage V Wilms’ tumor is defined as bilateral renal involvement at the time of initial diagnosis.

Note: For patients with bilateral involvement, an attempt should be made to stage each side according to the above criteria (stage I to III) on the basis of extent of disease prior to biopsy. The 4-year survival was 94% for those patients whose most advanced lesion was stage I or stage II; 76% for those whose most advanced lesion was stage III.

Treatment: Individualized therapy based on tumor burden

Stage I-IV Anaplasia

Children with stage I anaplastic tumors have an excellent prognosis (80-90% five-year survival). They can be managed with the same regimen given to stage I favorable histology patients.

Children with stage II through stage IV diffuse anaplasia, however, represent a higher-risk group.

These tumors are more resistant to the chemotherapy traditionally used in children with Wilms’ tumor (favorable histology), and require more aggressive regimens.

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