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Wilms tumor is a type of cancer that starts in the kidneys. It
is the most common type of kidney cancer in children. It is named for
Max Wilms, the German doctor who first wrote about it in 1899.
About the kidneys
To understand Wilms tumor, it helps to know something about
the kidneys.
The kidneys are 2 bean-shaped organs fixed to the back of the
belly (abdomen). They are shown in the picture below. Each kidney is
about the size of a fist. One kidney is just to the left and the other
just to the right of the backbone. The lower rib cage protects the
kidneys.
The kidney's main job is to filter the blood and get rid of
extra water, salt, and waste products in the form of urine. Urine
leaves the kidneys through long slender tubes called ureters. Each
kidney has a single ureter. The ureters empty into the bladder where
urine is stored until it is passed out of the body.
The kidneys help control blood pressure. They also help make
sure the body has enough red blood cells. They do this by making a
hormone (called erythropoietin), that tells the bone marrow to make
more red blood cells.
Although the kidneys are important, people can get by with
just one kidney. Today many people are living normal, healthy lives
with just one kidney.
Wilms tumors
Wilms tumors usually form only in one kidney, but in a small
number of cases they form in both. Wilms tumors are often found only
after they have grown quite large, but most are found before they have
spread to other organs. The average weight of a newly-found Wilms tumor
is about a pound. That's much larger than the kidney it started in.
Types of Wilms tumors
There are 2 main types of Wilms tumors. The type depends on
how the cells look under a microscope (this is called their histology).
Favorable
histology: Cells that look favorable show no anaplasia
(see below) and the chance of cure is good. More than 9 out of 10 Wilms
tumors have are of this type.
Unfavorable
histology: If a tumor looks unfavorable, it means that the
centers of the cells are very large and not the right shape. This is
called anaplasia.
The more anaplasia is found, the worse the chance for a cure.
Rarely, children can have other kinds of kidney cancer. The information here is only
about Wilms tumor and not other kinds of kidney cancer.
Last Medical Review: 10/07/2009
Last Revised: 10/07/2009
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