CHOC Children's

Wilms 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.

Approximately 500 children in the US are diagnosed with Wilms tumor each year.

The disease can occur at any age between infancy and 15 years, but, in most cases, the tumor is detected by the age of 3. This cancer affects males and females equally.

The tumor can be very large and it may spread (metastasize) to other body tissues. The most common site for Wilms tumor to metastasize is the lungs. Lesions may also occur, however, in the liver, the other kidney, brain, and/or bones. In approximately 5 to 10 percent of children with Wilms tumor, both kidneys are involved.

What causes Wilms tumor?

It is uncommon for Wilms tumor to run in families. Less than 2 percent of cases will have an affected relative. Most cases of Wilms tumor are considered sporadic (occur by chance) and are the result of genetic mutations that affect cell growth in the kidney. These mutations generally arise after birth, but, in some cases, children are born with a genetic alteration that predisposes them to cancer.

A small percentage of patients with Wilms tumor have one of three genetic syndromes, including the following:

  • WAGR syndrome - the acronym WAGR stands for the four diseases present in WAGR syndrome, including: Wilms tumor, aniridia (absence of the iris, the colored part of the eye), genitourinary malformations, and mental retardation. This is caused by loss or inactivation of a tumor suppressor gene called WT1 on chromosome #11. Tumor suppressor genes usually suppress the growth of tumors and control cell growth. When altered, they no longer control cell growth, and tumors may form.
  • Denys-Drash syndrome - this syndrome is characterized by kidney failure, genitourinary malformations, and tumors of the gonads (ovaries or testes). This is also caused by loss or inactivation of a tumor suppressor gene called WT1 on chromosome #11. Tumor suppressor genes usually suppress the growth of tumors and control cell growth. When altered, they no longer control cell growth, and tumors may form.
  • Beckwith-Wiedemann syndrome - this syndrome is characterized by large birthweight and a large liver, spleen, and tongue; low blood sugar in neonatal period, malformations around the ear, asymmetric growth of the body, abdominal wall defects near the navel (omphalocele), and tumors of the liver and adrenal glands. This is thought to be caused by an overactive copy of an oncogene on chromosome #11, called IGF2. Oncogenes control cell growth, but, if mutated, uncontrolled cell growth may result.

What are the symptoms of Wilms tumor?

The following are the most common symptoms of Wilms tumor. However, each child may experience symptoms differently. Symptoms may include:

  • a non-tender mass, or lump, felt or seen in the abdomen
  • swelling of the abdomen
  • veins that appear distended or large across the abdomen
  • blood in the urine (hematuria)
  • pain in the abdomen from pressure on other organs near the tumor
  • decreased appetite and weakness or tiredness
  • fever
  • high blood pressure (hypertension)

If a tumor is suspected in the child's abdomen, it is important not to apply pressure to this area. Careful bathing and handling of the child is necessary before and during any tumor evaluation. Rupture of the tumor may lead to cancer cells spreading to other tissues in the body.

These symptoms of Wilms tumor may resemble other medical conditions or serious illnesses. Always consult your child's physician for a diagnosis.

How is Wilms tumor diagnosed?

In addition to a complete medical history and physical examination, diagnostic procedures may include, but are not limited to, the following:

  • abdominal ultrasound - a diagnostic imaging technique that uses high- frequency sound waves and a computer to create images of blood vessels, tissues and organs; can provide an outline of the kidneys, the tumor, and determine if there are problems in the renal or other major veins in the abdomen. It can also determine if there are any lesions or tumors in the opposite kidney.
  • abdominal computed tomography scan (Also called a CT or CAT scan.) - a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than x-rays.
  • magnetic resonance imaging (MRI) - a diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body. MRI can determine if there are metastases (spreading), if there are any tumor cells in the lymph nodes, and/or if any other organs are involved. Wilms tumors can compress other organs in the area causing effects on their function.
  • chest x-ray - a diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film. A chest x-ray can determine if there are metastases (spreading) in the lungs.
  • blood and urine tests - to evaluate kidney and liver function.
  • biopsy - when a sample of tissue is removed and examined under a microscope. A biopsy of the tumor to evaluate cells, extent of disease, and diagnosis.
  • surgical removal of the tumor and kidney (nephrectomy) - surgery may be necessary for a definitive diagnosis and determining the extent of the disease.

Treatment for Wilms tumor:

Specific treatment for Wilms tumor will be determined by your child's physician based on:

  • your child's age, overall health, and medical history
  • extent of the disease
  • your child's tolerance for specific medications, procedures, or therapies
  • expectations for the course of the disease
  • your opinion or preference

Treatment for Wilms’ tumor depends on the tumor’s stage – how far and where the cancer has spread. This is called staging. The following stages are used for Wilms’ tumor:

  • Stage I – Cancer is found only in the kidney and can be completely removed by surgery.

  • Stage II – Cancer has spread beyond the kidney, to fat or soft tissue or blood vessels. The cancer can be completely removed by surgery.

  • Stage III – Cancer has spread within the abdomen and cannot be completely removed by surgery. The cancer may have spread to the lymph nodes (small bean-shaped structures found throughout the body that produce and store infection-fighting cells) near the kidney, blood vessels or the peritoneum (tissue that lines the abdomen and covers most organs in the abdomen).

  • Stage IV – Cancer cells spread to other parts of the body, such as the lungs, liver, bone and/or brain.

  • Stage V – Cancer cells are found in both kidneys when the disease is first diagnosed.

  • Recurrent – Recurrent disease means that the cancer has come back (recurred) after it has been treated. It may come back where it started or in another part of the body.

The three treatments used for patients with Wilms’ tumor include the following:


Surgery is a common treatment for Wilms’ tumor. Several different surgical approaches are used:

  • Partial nephrectomy – This approach removes the cancer and part of the kidney around the cancer. This operation is usually used only in special cases, such as when the other kidney is damaged or has already been removed.

  • Simple nephrectomy – This approach removes the entire kidney. The kidney on the other side of the body can take over filtering blood.

  • Radical nephrectomy – This approach removes the entire kidney with the tissues around it. Some lymph nodes in the area may also be removed.


Chemotherapy involves drugs used to kill cancer cells. Chemotherapy may be taken by pill, or it may be put into the body by a needle in a vein or muscle. Chemotherapy is called a “systemic treatment” because the drugs enter the bloodstream, travel through the body, and can kill cancer cells throughout the body. Chemotherapy given after an operation to remove the tumor is called “adjuvant therapy.”

When very high doses of chemotherapy are used to kill cancer cells, these high doses can destroy the blood-forming tissue in the bones (the bone marrow). If very high doses of chemotherapy are needed to treat the cancer, bone marrow may be taken from the bones before therapy and frozen until it is needed. Following chemotherapy, the bone marrow is given back through a needle in a vein. This is called autologous bone marrow reinfusion.

Radiation Therapy

Radiation therapy uses X-rays or other high-energy rays to kill cancer cells and shrink tumors. Radiation for Wilms’ tumor usually comes from a machine outside the body. Radiation may be used before or after surgery and/or chemotherapy.

Treatment may also include (alone or in combination):

  • biopsy of the tumor (if the tumor is too large or involved in surrounding structures to be removed ; a biopsy is also necessary for diagnosis and staging the disease)
  • medications (to control pain, hypertension, nausea, and infections)
  • blood pressure monitoring (essential when a kidney tumor is present)
  • continuous follow-up care (to determine response to treatment, detect recurrent disease, evaluate function of remaining kidney, and manage late effects of treatment)

Long-term outlook for Wilms tumor:

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

The factors for determining the prognosis and long-term survival of children with Wilms tumor include the following:

  • histology, favorable or unfavorable
  • extent of the disease
  • age and overall health of the child at diagnosis
  • size of the primary tumor
  • response to therapy
  • your child's tolerance of specific medications, procedures, or therapies
  • new developments in treatment

As with any cancer, prognosis and long-term survival can vary greatly from child to child.

Prompt medical attention and aggressive therapy are important for the best possible prognosis. Continued follow-up care is essential for the child diagnosed with Wilms tumor. Side effects of chemotherapy and radiation, as well as second malignancies, can occur in survivors of cancer. New methods are continually being discovered to improve treatment and to decrease side effects.

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It is important to remember the health information found on this website is for reference only not intended to replace the advice and guidance of your healthcare provider. Always seek the advice of your physician with any questions you may have regarding a medical condition. If you think you may have a medical emergency, call your physician or 911 immediately.

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