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% of all childhood cancers.
Approximately 400 children in the U.S. are diagnosed with a Wilms tumor each year. The disease can occur at any age between infancy and 15-years-old, but, in most cases, the tumor is detected by 3 years of age. 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% of children with Wilms tumor, both kidneys are involved.
Other tumors such as rhabdoid tumors of the kidney, clear cell sarcoma of the kidney and mesoblastic nephroma occur in the kidney but are not Wilms tumors and have different prognoses and treatment.
What Causes Wilms Tumor?
It is uncommon for Wilms tumor to run in families. Less than 2% of cases will have an affected relative. Most cases of Wilms 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:
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 intellectual disabilities. 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.
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.
This syndrome is characterized by large birth weight 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.
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:
A diagnostic imaging technique which 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.
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.
A diagnostic test which 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 & Urine Tests
Evaluate kidney and liver function
A sample of tissue is removed and examined under a microscope 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.
What Are the Symptoms of Wilms Tumor?
The following are the most common symptoms of a 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
- 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 Treated?
Specific treatment for Wilms tumor will be determined by your child's physician based on:
- Your child's age, overall health and medical history
- The extent of the disease
- Amount of tumor removed at initial surgery
- Appearance of the tumor under a microscope
- Your child's tolerance for specific medications, procedures or therapies
- Expectations for the course of the disease
- Your opinion or preference
Treatment may include (alone or in combination):
- Surgery (to remove all or part of the affected kidney and any involved structures)
- 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)
- Chemotherapy (to shrink the remaining tumor, or to treat metastasis and/or recurrent disease)
- Radiation (to shrink the remaining tumor or to treat metastasis and/or recurrent disease)
- Bone marrow transplant (used in patients with tumors that have recurred or do not respond to other treatment)
- 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)
What Are the Long-term Effects of Wilms Tumor?
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 a 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.