Wilms’ tumor, also called nephroblastoma, is the most common kind of kidney cancer in children. It makes up about 95 percent of all childhood kidney cancers and 6 percent of all childhood cancers. About 500 children in the United States are diagnosed with Wilms’ tumor each year, and most of them can be cured.

This disease was named for the surgeon who first identified it in 1899 (Max Wilms). It develops when cancerous cells grow in one or both of the kidneys, the two bean-shaped organs on each side of the spine in the abdomen. Wilms’ tumor usually starts when certain cells in the kidney multiply uncontrollably, growing into a cancerous mass.

Wilms’ tumor is usually diagnosed in children between ages two and three, though it can occur in infants as well as adults.

Learn more about primary kidney cancer in adults.  

Bilateral Wilms’ tumor

In children who have the tumors in both kidneys (bilateral), the tumors can develop at the same time, or a tumor can develop first in one kidney and later in the other.

Symptoms

A child with Wilms’ tumor may have no symptoms and feel and look healthy, because the tumor usually grows without pain. Typically, the tumor is detected as a lump in the abdomen, found by a parent or pediatrician during a routine checkup.

However, about one-quarter of children have symptoms. Those include:

  • blood in the urine
  • anemia
  • weight loss
  • fever

Risk Factors

Most children develop Wilms’ tumor due to a random genetic mutation, not from an inherited genetic mutation. However, about 1 to 2 percent of children with Wilms’ tumor have a family member or relative with the disease. Compared with most young patients, children with an inherited form of the disease have a higher risk of developing tumors at an earlier age, having tumors in both kidneys, and being born with other abnormalities.

Approximately 15 percent of children with Wilms’ tumor have other abnormalities, including:

  • reproductive or urinary problems
  • one side or part of the body that’s larger than the other (hemihypertrophy)
  • an abnormally small head (microcephaly)
  • syndromes that can cause problems with growth, genital development, and vision, like Beckwith-Wiedemann syndrome, Denys-Drash syndrome, and WAGR (which stands for Wilms’ tumor, aniridia, genitourinary abnormalities, mental retardation)

Doctors have not found a connection between environmental factors and Wilms’ tumor.