Wilms' Tumor (Kidney Tumor)

What is Wilms' tumor?

Wilms' tumor, also called nephroblastoma, is a malignant (cancerous) tumor originating in the cells of the kidney. It is the most common type of renal (kidney) cancer and accounts for about 6 percent of all childhood cancers. As with any cancer, prognosis and long-term survival can vary greatly from child to child, but most children with Wilms' tumor can be cured of the disease.

Wilms' tumor is unrelated to adult kidney cancer. The tumor usually affects a single kidney, but approximately 5-10 percent of children with Wilms' tumor have both kidneys involved.

Who is diagnosed with Wilms' tumor?

Wilms' tumor occurs in children up to about age 8. About 75 percent of cases occur before age 5, and the average age of children diagnosed with Wilms' tumor is 2 to 3 years old. For unknown reasons, Wilms' tumor affects more black children than white children.

The average age of diagnosis of Wilms' tumor in children depends upon whether one or both kidneys are affected:

  • If one kidney is affected (unilateral Wilms' tumor), the age at diagnosis usually is 42-47 months
  • If both kidneys are affected (bilateral Wilms' tumor), the age at diagnosis usually is 30-33 months

Most cases of Wilms' tumor occur by chance (sporadic). They are the result of mutations in cells in the kidneys that usually occur after birth. In some cases, however, a genetic defect increases the risk of Wilms' tumor.

Signs and symptoms of Wilms' tumor

Wilms' tumor is characterized by:

  • Abdominal swelling, often toward one side
  • Fever
  • Abdominal pain
  • Constipation
  • High blood pressure (hypertension)
  • Large swollen veins across the abdomen
  • Blood in the urine (hematuria)
  • Fatigue
  • Loss of appetite
  • Weight loss
  • Frequent urinary tract infections

Diagnosis of Wilms' tumor

After taking a complete medical history and doing a physical examination of your child, the physician may also order the following tests to determine if the cancer has spread (metastasized):

  • Abdominal ultrasound. This imaging test uses high-frequency sound waves and a computer to create pictures of internal organs, blood vessels and tissues.
  • Bone scan. This imaging test, which is used to detect bone cancer, uses a special radioactive material that is injected into a vein. The substance collects in areas of diseased bone and is sensed by special cameras that pick up radioactivity.
  • Abdominal computerized tomography scan (CT or CAT scan). This imaging test uses X-rays and computer technology to produce detailed cross-sectional images (slices) of the body, including the bones, muscles, fat and organs. It can show a mass in the kidneys and whether the cancer has spread to other organs such as the lungs.
  • Chest X-ray. This imaging test produces images of the heart, lungs and bones.
  • Magnetic resonance imaging (MRI). An MRI scan uses radio waves and strong magnets with computer technology. MRI shows more detailed images than CT and ultrasound and can help doctors see if the cancer has invaded one of the major blood vessels located near the kidney.
  • Blood and urine tests. These laboratory tests help evaluate kidney and liver function.
  • Biopsy. A sample of tissue is removed and examined under a microscope; this helps confirm the diagnosis and aids in the treatment plan.

Treatment for Wilms' tumor

The affected kidney and possibly adjoining lymph nodes may be surgically removed. In addition, Wilms' tumor is treated by chemotherapy and high-dose radiation to kill remaining cancer cells.

Proton therapy, a more targeted form of radiation therapy, is offered at Children's Hospital of Philadelphia as a treatment option for Wilms' tumor. This therapy is provided in partnership with Penn Medicine at the Roberts Proton Therapy Center. 

The overall cure rate for Wilms' tumor is 85 percent. As with any cancer, however, prognosis and long-term survival can vary greatly from child to child. Prompt medical attention and aggressive therapy are important for the best prognosis. Continuous follow-up care is essential for a child diagnosed with Wilms' tumor because side effects of radiation and chemotherapy may occur as well as second malignancy.

Surgery for Wilms' Tumor

Most children with Wilms tumor will require surgery as part of their treatment plan. At CHOP, your child will be treated by a multidisciplinary team including surgeons, oncologists, radiation oncologists and nurse practitioners, who work together to create a treatment plan specific to your child. You and your child will meet with the treatment team to ensure your family has an opportunity to build a trusting relationship with them. Scans are done prior to surgery to evaluate the extent of the tumor in the kidney and determine whether it has spread to other parts of the body, such as the lungs.

Late effects/cancer survivorship

Some children treated for Wilms' tumor develop complications many years later. Our Cancer Survivorship Program provides you and your child with information about the potential long-term effects of the specific treatment your child received and ways of monitoring and treating these effects.

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