Overview

About the kidneys

Wilms tumor is a type of childhood cancer that begins in the kidneys. Every person has two kidneys. They are bean-shaped organs located above the waist on both sides of the spine. They are closer to the back of the body than the front. The kidneys filter waste from the blood and make urine. As the kidneys develop in an unborn baby, some of the early cells will become glomeruli (balls of blood vessels that filter water, salt, and waste out of the blood) and some will become nephrons (the tubes through which the water, salt, and waste pass).

About Wilms tumor

If the early cells of the kidney do not develop into glomeruli or nephrons, groups of the immature cells may form in the kidneys when the baby is born. Usually, these cells mature by the time a child is three or four years old, but some may grow uncontrollably, forming a mass of immature cells. This mass is called a Wilms tumor, but it can also be called a nephroblastoma.

Wilms tumor is the most common type of kidney cancer in children and is very different from adult kidney cancer. Although Wilms tumor can develop in both kidneys (called bilateral), it usually occurs in only one (unilateral). Rarely, Wilms tumor develops in one kidney first and then the other. Wilms tumor is often found only after it has grown to a size of about eight ounces. (For comparison, a three-year-old child’s kidney usually weighs about two ounces.) About one out of four children with Wilms tumor have evidence that the tumor has spread either to the lung or liver when it is first diagnosed.

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Looking for More of an Overview?

If you would like additional introductory information, explore these related items on Cancer.Net:

• ASCO Answers Fact Sheet: Read a one-page fact sheet (available in PDF) that offers an easy-to-print introduction for this type of cancer.

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