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Wilms tumor (also called Wilms' tumor or nephroblastoma) is a type of
cancer that starts in the kidneys. It is the most common type of kidney
cancer that affects children. It is named after Max Wilms, a German
doctor who wrote one of the first medical articles about the disease in
1899.
About the kidneys
The kidneys are 2 bean-shaped organs fixed to the back wall of
the abdominal cavity (see 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 kidneys' main job is to filter the blood and rid the body of excess
water, salt, and waste products. The filtered waste products are
concentrated into urine. Urine leaves the kidneys through long, slender
tubes called ureters that connect to the bladder. Urine flows down the
ureters into the bladder, where it is stored until urination.
The kidneys also help make sure the body has enough red blood
cells. They do this by making a hormone called erythropoietin, which
tells the bone marrow to make more red blood cells.
Our kidneys are important, but we actually need less than 1
complete kidney to do all of the basic functions discussed above. Tens
of thousands of people in the United States are living normal, healthy
lives with just 1 kidney.
Wilms tumors
Wilms tumors may start anywhere in the kidneys. Most Wilms
tumors are unilateral, which means they affect only 1 kidney. In most
cases there is only one tumor, but in 5% to 10% of cases there is more
than one tumor in the same kidney. About 5% of children with Wilms
tumor have bilateral disease (cancer in both kidneys).
Wilms tumors often become quite large before they are noticed.
The average weight of a newly found Wilms tumor is about 1 pound --
many times larger than the kidney in which it developed. Most tumors
are found before they have spread (metastasize) to other organs.
Even though doctors may think a child has a cancer such as
Wilms tumor, they cannot be certain until a sample of the tumor is
looked at under a microscope.
Types of Wilms tumor
Wilms tumors are classified into 2 major types depending on
their histology (how they look under a microscope):
Favorable
histology: These Wilms tumor have a favorable appearance
under the microscope. While the cells aren't quite normal looking,
there is no anaplasia (see below). More than 90% of Wilms tumors have a
favorable histology. The chance of cure for these tumors is very good.
Unfavorable
histology (anaplastic Wilms tumor): These Wilms tumors
have an unfavorable appearance under the microscope. The look of the
cancer cells varies widely, and the nuclei (the central part of the
cell that contains the DNA) of the cells tend to be very large and
distorted. This is called anaplasia. The more anaplasia that is found,
the poorer the chance is for a cure.
Other Types of Kidney Tumors in
Children
About 90% of kidney tumors that occur in children are Wilms
tumors. Very rarely, children may develop other types of kidney tumors.
Mesoblastic
nephroma: This is a tumor that usually appears in the
first
few months of life. These tumors are usually curable with surgery.
Clear cell
sarcoma of kidney (CCSK): These tumors are much more
likely
to spread than Wilms tumors and are harder to cure. Treatment is
usually similar to the intensive treatment used for unfavorable
histology Wilms tumor.
Rhabdoid tumor
of the kidney: These tumors occur most often in infants.
They tend to spread to other parts of the body quickly, and most have
already spread at the time of diagnosis, which makes them hard to cure.
Treatment is usually similar to the intensive treatment used for
unfavorable histology Wilms tumor.
Renal cell
carcinoma: This is the most common type of kidney cancer
in
adults, although it accounts for a small number of kidney tumors in
children.
The rest of this document refers only to Wilms tumor.
Last Revised: 02/05/2008
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