Wilms' tumor is the most common form of kidney cancer in children under age 15. It is the second most common type of childhood solid tumor. About 500 Wilms' tumors cases are diagnosed each year. The average age of patients is 2 to 3 years old. More than 90 percent of children with this disease are cured.
The kidneys are two bean-shaped organs located on either side of the spine in the middle of the back that filter wastes from the blood and make urine. As the kidneys develop in the fetus, some of the early cells will become glomeruli and some nephrons. Glomeruli are balls of blood vessels that filter water, salt and waste out of the blood. Nephrons are the tubes through which these substances pass.
If the early cells of the kidney do not develop properly, groups of them may form in the kidneys when the baby is born. Usually, these cells mature by the time a child is 3 or 4. But the cells may start to grow out of control and form a mass of immature cells; this is a Wilms' tumor.
Wilms' tumor usually forms in just one kidney (unilateral Wilms' tumor), but can be bilateral, (affecting both kidneys) and is often found only after it has grown to a size of about 8 ounces (a normal kidney in a 3-year-old weighs about 2 ounces).
People need at least one kidney to live. The remaining kidney can take over the job of filtering wastes in the body.
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