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 400 children in the US are diagnosed with a 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 percent 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 percent 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:
- 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 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
- 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.