Wilms' tumor, also called nephroblastoma, is the most common form of kidney cancer in children. It develops when cancerous (malignant) kidney cells multiply out of control, eventually forming a mass. This mass usually is smooth and fairly round.
As it grows, Wilms' tumor changes the normal shape and appearance of the kidney. It also can destroy normal kidney tissue and cause bleeding into the urine. In some cases, the tumor eventually becomes noticeable as a firm, smooth lump in the child's side or abdomen. Without proper treatment, the cancer can spread to other organs—usually the lungs and liver.
Wilms' tumor is uncommon, accounting for just a small percentage of all childhood cancers. It is much more common in African American children than in white or Asian American children, and it is slightly more common in girls than in boys. In most cases, the tumor affects only part of one kidney. But sometimes, tumors affect both kidneys or occur in multiple parts of a kidney.
Specific genetic mutations have been identified in some patients with Wilms' tumors; having these mutations may mean a less favorable prognosis. Testing for these mutations can help doctors determine the best treatment.
Children with certain birth defects are more likely to develop Wilms' tumor, too. These include not having irises in the eyes and excessive growth on one side of the body.
Symptoms of Wilms' tumor include
- a firm lump or swelling in the child's abdomen or side that may not cause pain or discomfort
- abdominal pain
- blood in the urine
- high blood pressure, triggered when the tumor blocks the blood supply to the kidney.
Wilms' tumor often is found when a parent notices a lump or swelling while bathing or dressing his or her child. In most cases, the child is about 3 years old when the tumor is found.
The doctor will review your child's symptoms and medical history, as well as the mother's pregnancy history. If your child has obvious birth defects, the doctor will ask about your family's history of related problems, especially those affecting the genitals or urinary tract. The doctor also will ask if anyone in your family has had cancer. This is particularly important if any relatives had cancer at a very young age.
The doctor then will examine your child, checking his or her abdomen and genital area. This will be followed by
- basic blood and urine tests
- an ultrasound
- a computed tomography (CT) scan or magnetic resonance imaging (MRI) scan of the abdomen.
If these tests show signs of a kidney tumor, the doctor will refer you to a medical center with the facilities, staff, and experience to treat childhood cancer.
Before beginning treatment, your child will have more tests to find out if the tumor has spread (metastasized) to other parts of the body. These tests may include an x-ray, CT scan, or an MRI scan of the chest, and a radionuclide bone scan. Your child also will need a biopsy to confirm the diagnosis. During a biopsy, a small piece of the tumor is removed and examined in a laboratory to check for cancer cells.
After the cancer has been diagnosed, doctors will assign it a "stage." The stage indicates how far the disease has advanced. These are the stages of Wilms' tumor:
- Stage I. The cancer is confined to the kidney.
- Stage II. The cancer has spread beyond the kidney to nearby tissues.
- Stage III. The cancer has spread beyond the kidney to nearby tissues, and it cannot be removed completely with surgery.
- Stage IV. The cancer has spread to other parts of the body, such as the lungs, liver, bones, or brain.
- Stage V. The cancer involves both kidneys.
A Wilms' tumor will continue to grow until it is treated. Without treatment, this cancer 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, which describes how far the cancer has advanced. In general, children with a lower stage cancer need less treatment and have a better chance of being cured. However, almost all children with Wilms' tumor will need both surgery and chemotherapy.
There are two general approaches to the treatment of Wilms' tumors, both of which give favorable results. In one, doctors surgically remove the kidney (called a nephrectomy) and any cancer in nearby tissues, and then the patient has chemotherapy. In the other, the patient has chemotherapy first, followed by surgery. Having chemotherapy first can shrink the tumor, possibly making the surgery more successful.
Depending on the tumor's location and its response to chemotherapy, your child may need radiation therapy. For example, radiation therapy may be given if the surgeon cannot completely remove the tumor. Your child's doctor may also suggest radiation if the cancer has spread to the lungs. However, this may not be necessary if the lung tumors disappear with chemotherapy.
If both kidneys are affected by Wilms' tumor, treatment will attempt to spare at least part of one kidney so that your child does not need to have dialysis.
Genetic testing helps determine what type of treatment may be best for Wilms' tumor. Several new tumor vaccines have been developed that are successful in selected patients. Treatment at a specialized cancer center where these tests can be done is preferable.
When To Call a Professional
Call a doctor if your child develops an abnormal fullness or mass in the abdomen, even if he or she is not in pain. If a diagnosis of Wilms' tumor is made, it should be confirmed by a specialist in children's cancers. Whenever possible, a child with Wilms' tumor should be treated at a cancer center experienced in diagnosing and treating rare childhood disorders.
With proper treatment, most children with Wilms' tumor can be cured and will live for many years. However, secondary complications as a result of treatment may develop at some point. These include damage to the kidneys, heart, and liver. Other cancers may develop, too. That's why children deemed cured of Wilms' tumor must regularly see a doctor who will check for these complications.