Wilms tumor, or nephroblastoma, is a rare type of kidney cancer found most frequently in children ages 3 to 4. While the cause is unclear, researchers believe that the kidney cells develop errors in their DNA during the child's early development, resulting in a tumor that affects one or both kidneys. Although the defective cells that lead to Wilms tumor can be passed from parent to child, in most cases there is no familial link.
The condition, named for the German doctor who first described it in 1899, is the fourth most common pediatric cancer. Around 500 cases are diagnosed in the US each year, and most are curable.
Who Is At Risk for Wilms Tumor?
Birth defects: About one in every 10 cases of Wilms tumor occurs in children with specific birth defects: Children with Beckwith-Wiedemann syndrome (which results in abnormally large organs) and a few other specific, congenital conditions are at increased risk of disease and should be screened regularly.
Genetic risk: Children born to a parent with Wilms tumor have a slightly increased risk of disease, though most cases are not hereditary.
Symptoms of Wilms Tumor
Many children with this form of cancer show no sign of disease, which is why the average Wilms tumor is 1 pound at diagnosis. Those who do have symptoms may experience:
- A hard lump in the abdomen
- Stomach pain and swelling
- Blood in the urine
- High blood pressure
- Loss of appetite
Diagnosing and Categorizing Wilms Tumor
Diagnosis often begins with a physical examination, in which the doctor feels for lumps in the abdominal area. Diagnosis can be confirmed with:
- Imaging tests (ultrasound, MRI, and CT scans) can determine if Wilms tumor is present and, if so, what stage the cancer is in.
- Biopsy removes a portion of the tumor that can be examined to determine whether cancer is present and, if so, what type of Wilms tumor a patient has.
Depending on the characteristics of the tumor cells when they're viewed under a microscope, a pathologist will categorize the tumor as having either either favorable or unfavorable characteristics:
- Favorable: The tumor cells look abnormal but show no malignancy. Most Wilms tumors (at least 85 percent) fall in this category and are usually very treatable with current therapies.
- Unfavorable: The tumor cells tend to be very large and distorted. The more malignant properties in the tumor, the harder it is to cure. Unfavorable traits are found in only about 10 percent of Wilms tumor cases.
Stages of Wilms Tumor
After assessing the tumor, a physician must determine how far the cancer has progressed--an important step in prescribing treatment. The different stages are:
- Stage I: Cancer is found in only one kidney and the growth can be completely removed by surgery. Almost half of all Wilms tumor cases are caught at this stage.
- Stage II: Cancer has spread beyond the kidneys but lymph nodes remain disease-free and surgery can effectively remove the tumor.
- Stage III: The disease has not spread beyond the abdomen, but surgery can’t completely remove it all. (In this case, radiation or chemotherapy may also be used. See Treatment of Wilms Tumor for more information.)
- Stage IV: Cancer has spread to other organs, including the lungs or bone, or to more distant lymph nodes.
- Stage V: Cancer is found in both kidneys (bilateral).
Treatment for Wilms Tumor
Surgery is almost always used to treat Wilms tumor, regardless of the cancer's stage and characteristics: Typically, the entire kidney, ureter, adrenal gland, and fatty tissue in the affected area are removed. Chemotherapy and radiation therapy may also be recommended. Together, these approaches yield a 85-90 percent cure rate. Read our full-length article on Wilms Tumor treatment for more information.
Albala D, Morey A, Gomella L, & Stein J. (2011). Wilms tumor and neuroblastoma. Oxford American Handbook of Urology.