Wilms’ tumor, also called nephroblastoma, is the most common type of kidney cancer found in children. It accounts for approximately 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, the majority of which can be cured.

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

When these tumors occur in only one kidney, they are called unilateral tumors. In a small number of cases, Wilms’ tumor can form in both kidneys (bilateral tumors). In children with bilateral disease, tumors can develop at the same time, or a tumor can develop first in one kidney and later in the other.


Wilms’ tumor is most frequently diagnosed in children between the ages of two and three, though it can occur in infants as well as adults. Typically, the tumor is detected as a lump in the abdomen, found by a parent or by a pediatrician during a routine check-up.

The tumor usually grows without any accompanying pain, so a child with Wilms’ tumor may feel and appear healthy. However, in about one-quarter of children, the disease is accompanied by symptoms such as blood in the urine, anemia, weight loss, and fever.

Risk Factors

Most children develop Wilms’ tumor due to a random, sporadic genetic mutation — not from an inherited gene. However, about 1 to 2 percent of children with Wilms’ tumor have a family member or relative with the disease. Compared with children who have sporadic cases, children with an inherited form of the disease have a higher risk of developing tumors at an earlier age, having bilateral tumors, and being born with other congenital abnormalities.

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

  • reproductive or urinary problems
  • hemihypertrophy, in which one side or part of the body is larger than the other
  • microcephaly, in which a child’s head is abnormally small
  • syndromes such as Beckwith-Wiedemann syndrome, Denys-Drash syndrome, and WAGR (Wilms’ tumor, aniridia, genitourinary abnormalities, mental retardation)

To date, doctors have not identified a connection between environmental factors and Wilms’ tumor.