Wilms' tumor is one of the most common tumors of the abdomen in children and the most common type of kidney tumor. The exact cause of tumor formation in most children is unknown.

It is associated with certain birth defects including urinary tract abnormalities, absence of the iris (aniridia), and hemihypertrophy (enlargement of one side of the body). It is more common among some siblings and twins, which suggests a possible genetic cause.

The tumor may become quite large, but usually remains encapsulated (self-enclosed). It may spread to other body tissues, especially the lungs.

The disease is estimated to occur in about 1 out of 200,000 to 250,000 children. The peak time of occurrence is at 3 years old, and Wilms' tumor is rare after the age of 8 years.

• Abdominal pain
• Swelling in the abdomen (abdominal hernia or mass)
• Blood in the urine (occurs in less than 1/4 of children)
• Fever
• Loss of appetite
• Nausea
• Vomiting
• General discomfort or uneasiness (malaise)
• High blood pressure
• Constipation
• Increased growth on only one side of the body (hemihypertrophy)

Note: Abnormal urine color may also be associated with this disease. A missing iris of the eye (aniridia) is a birth defect that is sometimes associated with Wilms' tumor.

CAUTION: Avoid palpation (prodding or pushing) of the abdomen, and use care during bathing and handling to avoid injury to the tumor site.

Special emphasis is placed on the history and physical exam -- looking for a family history of cancer and for associated birth defects in the child. The physical examination reveals an abdominal mass. High blood pressure may also be present.

Tests include:

• CBC (may show anemia)
• BUN
• Creatinine
• Creatinine clearance (may be decreased)
• Urinalysis (blood or protein in urine)
• Abdominal ultrasound
• Abdominal X-ray
• Chest X-ray (may demonstrate metastasis)
• Intravenous pyelogram (distortion of the kidney)
• CT scan of the abdomen (abdominal mass arising from kidney)

Clinical staging of the tumor is done to determine the extent of the tumor and to maximize the effectiveness of treatment plans. Surgical exploration and removal of the tumor is scheduled as soon as possible.

Regional lymph nodes, abdominal organs, and other tissues are examined and removed if the tumor has spread to those areas. Radiation therapy and chemotherapy will often be started after surgery, depending on the stage of the tumor.

With treatment, the disease has a high cure rate. Children with a localized tumor have a 90% cure rate when treated with surgery and chemotherapy; or with surgery, radiation, and chemotherapy combined.

Spread of the tumor to the lungs, liver, bone, or brain is the most worrisome complication. High blood pressure and kidney damage may occur as the result of the tumor or its treatment. Removal of Wilms' tumor that is present in both kidneys may leave the patient with borderline kidney function.

Call your health care provider if you discover an abdominal mass in your child's abdomen, blood in the urine, or other symptoms suggestive of Wilms' tumor.

Call your health care provider if symptoms worsen or new symptoms develop during or after treatment for Wilms' tumor, particularly cough, chest pain, weight loss, or persistent fevers.

For children with a known high risk of Wilms' tumor, screening with ultrasound of the kidneys may be recommended.