Wilms (/vɪlmz/) tumor, Wilms’ tumor, or nephroblastoma is a cancer of the kidneys that typically occurs in children, rarely in adults. It is named after Dr. Max Wilms, the German surgeon (1867–1918) who first described it.
Approximately 500 cases are diagnosed in the U.S. annually. The majority (75%) occur in otherwise normal children; a minority (25%) are associated with other developmental abnormalities. It is highly responsive to treatment, with about 90% of patients surviving at least five years.
Signs and symptoms
Typical signs and symptoms of Wilms’ tumor include the following:
- an abnormally large abdomen
- abdominal pain
- nausea and vomiting
- blood in the urine (in about 20% of cases)
- high blood pressure in some cases (especially if synchronous or metachronous bilateral kidney involvement)
Most nephroblastomas are on one side of the body only and are found on both sides in less than 5% of cases, although patients with Denys-Drash syndrome mostly have bilateral or multiple tumors. They tend to be encapsulated and vascularized 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 puts the patient at risk of bleeding 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:
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. Dysfunction is caused when the tumor compresses the normal kidney parenchyma.
The mesenchymal component may include cells showing rhabdomyoid differentiation or 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)
Mutations of the WT1 gene on chromosome 11p13 are observed in approximately 20% of Wilms tumors. At least half of the Wilms tumors with mutations in WT1 also carry mutations in CTNNB1, the gene encoding the proto-oncogene beta-catenin.
A gene on the X chromosome, WTX, is inactivated in up to 30% of Wilms tumor cases, according to research published in 2007.
Most cases do not have mutations in any of these genes.
The first sign is normally a painless abdominal tumor that can be easily felt by the doctor. An ultrasound scan, computed tomography scan, or MRI scan is done first. A tumor biopsy is not typically performed due to the risk of creating fragments of cancer tissue and seeding the abdomen with malignant cells.
Staging is a standard way to describe the extent of spread of Wilms tumors, and to determine prognosis and treatments. Staging is based on anatomical findings and tumor cells pathology.
Stage I (43% of patients)
Stage I Wilms tumor, all 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 extrarenal or renal sinus lymph-vascular spaces
- No residual tumor apparent beyond the margins of excision.
- Metastasis of tumor to lymph nodes not identified.
Stage II (23% of patients)
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.
– Extensive tumor involvement of renal sinus soft tissue.
Stage III (20% of patients)
Stage III Wilms tumor, 1 or more of the following criteria must be met:
- Inoperable primary tumor.
- Lymph node metastasis.
- Tumor is present at surgical margins.
- Tumor spillage involving peritoneal surfaces either before or during surgery, or transected tumor thrombus.
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.
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 overall 5-year survival is estimated to be approximately 90%, but for individuals the prognosis is highly dependent on individual staging and treatment. Early removal tends to promote positive outcomes.
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).
Statistics may sometimes show more favorable outcomes for more aggressive stages than for less aggressive stages, which may be caused by more aggressive treatment and/or random variability in the study groups. Also, a stage V tumor is not necessarily worse than a stage IV tumor.