Wilms' tumor is a type of kidney cancer]]> that predominantly affects children. It usually occurs in the first five years of life, especially around ages three and four. In most cases, Wilms' tumor affects only one of the two kidneys. The frequency of this tumor is 1 in 200,000-250,000 children.

Wilms' tumor is generally divided into two types based on how it looks under the microscope. Favorable types of Wilms' tumor generally have a better outcome and require less aggressive treatment. The unfavorable or anaplastic histology of Wilms' Tumor is still curable, but requires more aggressive chemotherapy and higher doses of radiation therapy. Despite the more aggressive therapies, survival is generally more limited.


Kidneys and Renal Vessels
© 2009 Nucleus Medical Media, Inc.


In the fetus, some of the cells that are supposed to grow into mature kidneys stay as fetal kidney cells. Clusters of these cells sometimes remain after birth. If they do not mature within three or four years, they may grow out of control. A large mass of these cells forms and may develop into a Wilms' tumor.

A small percentage of children with Wilms' tumors have inherited an abnormal gene from one parent. This gene greatly increases the chance that some of their kidney cells will turn into a Wilms' tumor. Some other children have certain birth defects that increase their risk for Wilms' tumor. However, many children with Wilms' tumors do not have any known inherited gene changes or birth defects. Researchers do not know why these children have some kidney cells that do not mature properly.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. One risk factor for Wilms' tumor is having a family member with a Wilms' tumor. Also, certain birth defects increase the risk of a Wilms' tumor. These include:

  • WAGR—a syndrome that includes:
    • W ilms' tumor
    • A niridia—completely or partly missing iris (colored part) of the eyes
    • G enitourinary abnormalities—defects of the kidneys, urinary tract, penis, scrotum, testicles, clitoris, or ovaries
    • Mental R etardation
  • Beckwith-Wiedemann syndrome—larger than normal tongue and internal organs; one arm or leg may be larger than the other
  • Denys-Drash syndrome—absence of the penis, scrotum, and testicles
  • Hemihypertrophy—one side of the body larger is than the other
  • Other genetic defects, including defects on chromosome 11.
Patients with these abnormalities should be regularly screened for Wilms’ tumor during childhood.


The first noticeable symptom is usually a large lump or hard mass in the abdomen. Other symptoms may include:

  • Stomach pain
  • Fever
  • Blood in the urine
  • High blood pressure]]>
  • Loss of appetite, nausea, vomiting, and constipation
  • Erythrocytosis (a condition where there are too many red cells in the blood) may also be a presenting sign your doctor finds when taking a blood test. This is because Wilms’ tumor makes a protein that causes increased production of red cells.

Wilms' tumors may grow larger without causing any pain or other symptoms.



The doctor will ask about your child’s symptoms and medical history, and perform a physical exam. Blood and urine tests may be done.

Your child will need one or more of the tests below to look for tumors. These tests provide pictures of the kidney, surrounding blood vessels, and other organs to which the cancer may have spread:

  • Ultrasound]]> —a test that uses sound waves to examine the kidneys.
  • ]]>CT scan]]> —a type of x-ray that uses a computer to make pictures of the inside of the body. In some cases, a dye is first injected into a vein. This dye makes structures in the body more visible on x-ray.
  • ]]>MRI scan]]> —a test that uses magnetic waves to make pictures of the inside of the body.
  • ]]>Chest x-ray]]> —a test that uses radiation to look for spread of cancer to the lungs.
  • Bone scan—a small amount of a radioactive material is injected into a vein to highlight any cancer that may have spread to the bones.
  • ]]>Biopsy]]> —removal of a sample of tissue to test for cancer cells. In Wilms’ tumor, the biopsy may actually be a major surgical procedure to remove the kidney.

Except for removal of the kidney, these tests are not invasive but require the child to remain still. Sedation may be needed.

Children who have risk factors for Wilms' tumor should have a physical exam with a specialist and an ultrasound every three months until age six or seven. This screening should be done even if they do not have symptoms. It can help find tumors while they are small and have not yet spread to other parts of the body.



Wilms' tumor can be cured in most children. The specific treatment depends on if the cancer has spread beyond the kidney to other parts of the body, and if so, how far. The process for determining this, called staging, uses the results of the diagnostic tests. Tumor size, cell type, whether the tumor is favorable or unfavorable, and your child’s age and health are also considered in choosing treatment.

In general, tumors with favorable histology are treated only with combinations of chemotherapy, and those with unfavorable patterns or which are recurrent, often require the addition of radiation therapy.

Treatment may include:


The main treatment for Wilms' tumor is a type of surgery called nephrectomy. This is the removal of the kidney with the tumor. The tissue around the kidney may also be removed, as well as some nearby lymph nodes. The remaining kidney will take care of all of the needed functions for the body.


Chemotherapy]]> is the use of drugs to kill cancer cells. Chemotherapy can be given in many forms including: pill, injection, and via a catheter placed in a blood vessel. The drugs enter the bloodstream and travel through the body killing mostly cancer cells, but also some healthy cells.

Radiation Therapy

This is the use of ]]>radiation]]> to kill cancer cells and shrink tumors. Radiation may be:

  • External radiation therapy—radiation directed at the tumor from a source outside the body

Radiation of Tumor

Radiation of Tumor
© 2009 Nucleus Medical Media, Inc.


Currently, there is no known way to prevent Wilms' tumor.