Wilms' tumor, also called nephroblastoma, is the most common form of kidney cancer to affect children. Wilms' tumor develops when cancerous (malignant) kidney cells multiply out of control, and eventually form a firm, grayish or tan mass (tumor). This mass usually is smooth and fairly round. As it grows larger, Wilms' tumor changes the normal shape and appearance of the kidney. It also can destroy areas of normal kidney tissue, and can cause bleeding into the urine. In some cases, the tumor eventually grows so large that it becomes noticeable as a firm, smooth lump in a child's side or abdomen. Without proper treatment, Wilms' tumor has the potential to spread outside the kidney, most commonly to the lungs and the liver.

Wilms' tumor is uncommon. Only about 500 new cases are diagnosed in the United States each year. It accounts for 5% to 6% of all childhood cancers in the United States. Wilms' tumor is much more common in African-American children than in Caucasians or Asian-Americans, and it is slightly more common in girls than in boys. In most cases, the tumor affects only one area in one kidney. Occasionally, tumors will affect both kidneys or will occur in multiple areas inside the kidney.

Children with certain birth defects are more likely to develop Wilms' tumor. These birth defects include the absences of the irises of the eyes (aniridia) and excessive growth on one side of the body, called hemihypertrophy.

Symptoms of Wilms' tumor can include:

• A firm lump or swelling in the child's abdomen or side. Often, this lump does not cause pain or discomfort.
• Abdominal pain
• Vomiting
• Blood in the urine
• High blood pressure (hypertension), which is triggered when the tumor blocks the blood supply to the kidney

Wilms' tumor often is discovered when a parent notices a mass while bathing or dressing a child, most commonly a child who is about 3 years old.

The doctor will review your child's symptoms and medical history and the mother's pregnancy history. If your child has obvious birth defects, the doctor will ask questions about your family's history of related problems, especially those involving the genitals or urinary tract. The doctor also will review your family history of Wilms' tumor and other types of cancer. This is particularly important if you have relatives who developed cancer at a very young age.

The doctor then will examine your child, paying special attention to his or her abdomen and genital area. This will be followed by basic blood and urine tests, an ultrasound, and a computed tomography (CT) scan or magnetic resonance imaging (MRI) scan of the abdomen.

If these preliminary diagnostic tests show signs of a kidney tumor, the doctor will refer you to a major medical center that has the facilities, personnel and experience to treat childhood cancer. Before beginning cancer treatment, your child will have further tests to find out if the tumor has spread (metastasized) to other areas of the body. These tests may include chest X-rays, a CT scan or an MRI scan of the chest, and a radionuclide bone scan. Ultimately, your child also will need a biopsy of the tumor area to confirm the diagnosis. In a biopsy, a small piece of the tumor is removed and examined in a laboratory.

A Wilms' tumor will continue to grow until it is treated. Without proper treatment, this cancer eventually can spread to the lungs, liver and other parts of the body.

There is no way to prevent Wilms' tumor.

Treatment for Wilms' tumor depends on the tumor's stage — how far and where the cancer has spread. In general, children with a lower stage of disease have a better chance of being cured, and they require less treatment. However, almost all children with Wilms' tumor will require both surgery and chemotherapy. Surgery usually is done first, both to confirm the diagnosis and to remove all or as much of the tumor as possible. If the tumor cannot be removed completely, radiation therapy also may be given.

The stages of Wilms tumor are:

• Stage I — Cancer is limited to the kidney and can be removed completely by surgery. Treatment consists of surgery to remove the entire kidney (called a nephrectomy) followed by chemotherapy.



• Stage II — Cancer has spread beyond the kidney to nearby tissues. Surgery can remove most of the tumor, but microscopic amounts are left behind. Treatment consists of surgery to remove the entire kidney followed by chemotherapy and, in some cases, radiation.



• Stage III — Cancer has spread beyond the kidney to nearby tissues, and it cannot be removed completely with surgery. Treatment usually consists of surgery followed by radiation and chemotherapy. Occasionally, chemotherapy or radiation is given prior to surgery in the hopes that shrinking the tumor will make surgery more successful.



• Stage IV — Cancer has spread to other parts of the body, such as the lungs, liver, bones or brain. Treatment usually consists of surgery followed by radiation plus chemotherapy.



• Stage V — In this stage, Wilms' tumor involves both kidneys. Treatment often attempts to spare part of one of the kidneys, so that dialysis is not necessary.

Call the doctor if your child develops an abnormal fullness or mass in the abdomen, even if there is no abdominal discomfort.

With proper treatment, most children with Wilms' tumor can be cured of cancer. Long-term survival rates generally are greater than 90%.

National Cancer Institute (NCI)
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American College of Surgeons (ACS)
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American Academy of Pediatrics (AAP)
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American Society of Clinical Oncology
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