Wilms Tumor - Childhood: Overview

This section has been reviewed and approved by the Cancer.Net Editorial Board, 06/2014

ON THIS PAGE: You will find some basic information about this disease and the parts of the body it may affect. This is the first page of Cancer.Net’s Guide to Wilms Tumor. To see other pages, use the menu on the side of your screen. Think of that menu as a roadmap to this full guide.

Wilms tumor is a type of cancer that begins in a child’s kidney. 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, which are balls of blood vessels that filter water, salt, and waste out of the blood. Others will become nephrons, which are the tubes through which the water, salt, and waste pass. If the early cells of the kidney do not develop into glomeruli or nephrons, clusters 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; 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. Wilms tumor usually occurs in only one kidney, called unilateral, although it can develop in both kidneys, called bilateral. 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—about four times the weight of a healthy three-year-old child’s kidney. 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.

Looking for More of an Overview?

If you would like additional introductory information, explore these related items. Please note these links will take you to other sections on Cancer.Net:

  • ASCO Answers Fact Sheet: Read a one-page fact sheet (available as a PDF) that offers an easy-to-print introduction to this type of cancer.
  • Cancer.Net Patient Education Video: View a short video led by an ASCO expert in childhood cancers that provides basic information and areas of research.

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