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 two prognostic groups based on pathologic characteristics:
Favorable – Contains well developed components mentioned above
Anaplastic – Contains diffuse anaplasia (poorly developed cells)

Molecular biology and related conditions
Mutations of the WT1 gene which is located on the short arm of chromosome 11 (11p13) are observed in approximately 20% of Wilms tumors, the majority of them being inherited from the germline, while a minority are acquired somatic mutations. In addition at least half of the Wilms tumors with mutations in WT1 also carry acquired somatic mutations in CTNNB1, the gene encoding the proto-oncogene beta-catenin. This latter gene is found on short arm of chromosome 3 (3p22.1). Most cases do not have mutations in any of these genes. An association with H19 has been reported. H19 is a long noncoding RNA located on the short arm of chromosome 11 (11p15.5). Diagnosis
The majority of people with Wilms tumor present with an asymptomatic abdominal mass which is noticed by a family member or healthcare professional. Renal tumors can also be found during routine screening in children who have known predisposing clinical syndromes. The diagnostic process includes taking a medical history, a physical exam, and a series of tests including blood, urine, and imaging tests.Once Wilms tumor is suspected, an ultrasound scan is usually done first to confirm the presence of an intrarenal mass.
Extensive tumor involvement of renal sinus soft tissue.In Stage III (20% of cases), 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. The tumor has been biopsied prior to removal or there is local spillage of tumor during surgery, confined to the flank.Stage IV (10% of cases) Wilms tumor is defined by the presence of hematogenous metastases (lung, liver, bone, or brain), or lymph node metastases outside the abdominopelvic region.Stage V (5% of cases) Wilms tumor is defined by bilateral renal involvement at the time of initial diagnosis. 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. Treatment and prognosis
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.