Wilms tumor is the most common malignant renal tumor of childhood, with approximately 500 new cases per year in the United States. The mean age at diagnosis is 3 to 3.5 years of age, and no gender predilection is apparent. A hereditary form of Wilms tumor may be associated with bilateral presentation and younger age at onset. Many congenital anomalies are associated with Wilms tumor, including sporadic aniridia, hemihypertrophy, and genitourinary abnormalities. Patients with the WAGR (Wilms tumor, aniridia, genitourinary malformation, mental retardation) syndrome have Wilms tumor as a manifestation of the syndrome itself, resulting from a germline deletion at chromosome 11p. Patients with Beckwith-Wiedemann syndrome and some other overgrowth syndromes are at increased risk for developing Wilms tumor and should be screened with periodic renal imaging.
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Most children with Wilms tumor are brought to medical attention because they have an abdominal mass that is discovered by their parents. Although many children do not have complaints at the time that the mass is first noted, associated symptoms may include abdominal pain, fever, hypertension, and hematuria.
An abdominal ultrasound or computed tomography (CT) scan can usually distinguish an intrarenal mass from a mass in the adrenal gland or other surrounding structures. Evaluation of the inferior vena cava is crucial because the tumor may extend from the kidney into the vena cava. A complete blood count, urinalysis, liver and renal function studies, and a chest radio-graph (to identify pulmonary metastases) should be obtained. In most cases, a CT scan of the chest, abdomen, and pelvis is obtained. The diagnosis is confirmed by histologic examination of the tumor. Although most cases of Wilms tumor are classified as favorable histology, the presence of anaplasia is predictive of a worse prognosis and is considered unfavorable.
The differential diagnosis of Wilms tumor includes hydronephrosis and polycystic disease of the kidney; benign renal tumors, such as mesoblastic nephroma and hamartoma; and other malignant tumors, such as renal cell carcinoma, neuroblastoma, lymphoma, and retroperitoneal rhabdomyosarcoma.
The timing of nephrectomy for unilateral, resectable Wilms tumor remains controversial. The North American approach is for immediate nephrectomy followed by adjuvant chemotherapy, whereas the European approach is to make a diagnosis by imaging and sometimes a biopsy, give neoadjuvant chemotherapy followed by surgery and then adjuvant chemotherapy (plus radiation therapy, as indicated). The overall survival is comparable regardless of the approach. The Children’s Oncology Group protocols for Wilms tumor with favorable histologic findings generally include vincristine and actinomycin, with or without doxorubicin. Radiation therapy is reserved for a minority of patients depending on stage, presence of metastases, response to therapy, and LOH status.
Bilateral Wilms tumor is present in about 5% of children on initial presentation, whereas recurrent disease affects the opposite kidney in 4% to 5% of patients. Treatment for patients with bilateral Wilms tumor should be individualized to retain as much normal kidney as possible.
Survivors of Wilms tumor are at risk for several late effects, including cardiomyopathy, scoliosis, hypertension and prehypertension, renal and bladder insufficiency, pulmonary dysfunction, hepatic dysfunction, infertility, and second malignancies. Patients with bilateral Wilms tumor are sometimes left with renal insufficiency or failure. Female survivors may have complicated pregnancies and deliveries.