Wilms' tumor is a cancerous tumor of the kidney that usually occurs
in young children.
When an unborn baby is developing, the kidneys are formed from primitive
cells. Over time, these cells become more specialized. The cells mature
and organize into the normal kidney structure. Sometimes, clumps of these
cells remain in their original, primitive form. If these more primitive
cells begin to multiply after birth, they may ultimately form a large mass
of abnormal cells. This is known as a Wilms' tumor. Wilms'
tumor may occur in only one or in both kidneys. About 7 percent of all
cases of Wilms' tumor occur bilaterally (in both kidneys
Wilms' tumor is a type of malignant tumor. This means that it is
made up of cells that are significantly immature and abnormal. These cells
are also capable of invading nearby structures within the kidney and
traveling out of the kidney into other structures. Malignant cells can
even travel through the body to invade other organ systems, most commonly
the lungs and brain. These features of Wilms' tumor make it a type
that, without treatment, would eventually cause death. However, advances
in medicine between the 1980s and the early 2000s have made Wilms'
tumor a very treatable form of cancer.
Wilms' tumor occurs almost exclusively in young children. The
average patient is about three years old. Females are only slightly more
likely than males to develop Wilms' tumors. In the United States,
Wilms' tumor occurs in about eight children per million in white
children under the age of 15 years. Wilms' tumor makes up about 6
percent of all childhood cancers and ranks as the second most frequent
cancerous abdominal tumor in children. The rate is higher among African
and lower among Asian Americans. Wilms' tumors are found more
commonly in patients with other types of birth defects. These defects
include the following:
Causes and symptoms
The cause of Wilms' tumor is not as of 2004 completely understood.
Because 15 percent of all patients with this type of tumor have other
inherited defects, it seems clear that at least some cases of
Wilms' tumor may be due to an inherited alteration. It appears that
the tendency to develop a Wilms' tumor can run in families. In
fact, about 1.5 percent of all children with a Wilms' tumor have
members who have also had a Wilms' tumor. The genetic mechanisms
associated with the disease are unusually complex.
Some patients with Wilms' tumor experience abdominal
, high blood pressure, or blood in the urine. However, the parents of many
children with this type of tumor are the first to notice a firm, rounded
mass in their child's abdomen. This discovery is often made while
bathing or dressing the child and frequently occurs before any other
symptoms appear. Rarely, a Wilms' tumor is diagnosed after there
has been bleeding into the tumor, resulting in sudden swelling of the
abdomen and a low red blood cell count (anemia).
About 5 percent of Wilms' tumor cases involve both kidneys during
the initial evaluation. The tumor appears on either side equally. When
pathologists look at these tumor cells under the microscope, they see
great diversity in the types of cells. Some types of cells are associated
with a more favorable outcome in the patient than others. In about 15
percent of cases, physicians find some degree of cancer spread
(metastasis). The most common sites in the body where metastasis occurs
are the liver and lungs.
Researchers have found evidence that certain types of lesions occur before
the development of the Wilms' tumor. These lesions usually appear
in the form of stromal, tubule, or blastemal cells.
Children with Wilms' tumor generally first present to physicians
with a swollen abdomen or with an obvious abdominal mass. The physician
may also find that the child has
, bloody urine, or abdominal pain. The physician will order a variety of
tests before imaging is performed. These tests mostly involve blood
analysis in the form of a white blood cell count, complete blood count,
, and serum calcium evaluation. Liver and kidney function testing will
also be performed as well as a urinalysis.
Initial diagnosis of Wilms' tumor is made by looking at the tumor
using various imaging techniques. Ultrasound,
scans (CT scans) and
magnetic resonance imaging
(MRI scans) are helpful in diagnosing Wilms' tumor. Intravenous
pyelography, in which a dye injected into a vein helps show the structures
of the kidney, can also be used in diagnosing this type of tumor. Final
diagnosis, however, depends on obtaining a tissue sample from the mass
(biopsy) and examining it under a microscope in order to verify that it
has the characteristics of a Wilms' tumor. This biopsy is usually
done during surgery to remove or decrease the size of the tumor. Other
studies (chest x rays, CT scan of the lungs, bone marrow biopsy) may also
be done in order to see if the tumor has spread to other locations.
Treatment for Wilms' tumor almost always begins with surgery to
remove or decrease the size of the kidney tumor. Except in patients who
have tumors in both kidneys, this surgery usually requires complete
removal of the affected kidney. During surgery, the surrounding lymph
nodes, the area around the kidneys, and the entire abdomen will also be
examined. While the tumor can spread to these surrounding areas, it is
less likely to do so compared to other types of cancer. In cases where the
tumor affects both kidneys, surgeons will try to preserve the kidney with
the smaller tumor by removing only a portion of the kidney, if possible.
Additional biopsies of these areas may be done to see if the cancer has
spread. The next treatment steps depend on whether the cancer has spread
and if it has what other sites are involved. Samples of the tumor are also
examined under a microscope to determine particular characteristics of the
cells making up the tumor.
Information about the tumor cell type and the spread of the tumor is used
in deciding the best kind of treatment for a particular patient. Treatment
is usually a combination of surgery, medications used to kill cancer cells
), and x rays or other
high-energy rays used to kill cancer cells (radiation therapy). These
therapies are called adjuvant therapies, and this type of combination
therapy has been shown to substantially improve outcome in patients with
Wilms' tumor. It has long been known that Wilms' tumors
respond to radiation therapy. Likewise, some types of chemotherapy have
been found to be effective in treating Wilms' tumor. These
effective drugs include dactinomycin, doxorubicin, vincristine, and
cyclophosphamide. In rare cases, bone marrow transplantation may be used.
The National Wilms' Tumor Study Group developed a staging system to
describe Wilms' tumors. All of the stages assume that surgical
removal of the tumor has occurred. Stage I involves favorable
Wilms' tumor cells and is usually treated successfully with
combination chemotherapy involving dactinomycin and vincristine and
without abdominal radiation therapy. Stage II tumors involving a favorable
histology (cell characteristics) are usually treated with the same therapy
as Stage I. Stage III tumors with favorable histology are usually treated
with a combination chemotherapy with doxorubicin, dactinomycin, and
vincristine along with radiation therapy to the abdomen. Stage IV disease
with a favorable histology is generally treated with combination
chemotherapy with dactinomycin, doxorubicin, and vincristine. These
patients usually receive abdominal radiation therapy and lung radiation
therapy if the tumor has spread to the lungs.
In the case of Stage II through IV tumors with unfavorable, or anaplastic,
cells, then the previously-mentioned combination chemotherapy is used
along with the drug cyclophosphamide. These patients also receive lung
radiation therapy if the tumor has spread to the lungs. Another type of
tumor cell can be present in Stages I through IV. This cell type is called
clear cell sarcoma of the kidney. If this type of cell is present, then
patients receive combination therapy with vincristine, doxorubicin, and
dactinomycin. All of these patients receive abdominal radiation therapy
and lung radiation therapy if the tumor has spread to the lungs.
The prognosis for patients with Wilms' tumor is quite good,
compared to the prognosis for most types of cancer. The patients who have
the best prognosis are usually those who have a small-sized tumor, a
favorable cell type, are young (especially under two years of age), and
have an early stage of cancer that has not spread. Modern treatments have
been especially effective in the treatment of this cancer. Patients with
the favorable type of cell have a long-term survival rate of 93 percent,
whereas those with anaplasia have a long-term survival rate of 43 percent
and those with the sarcoma form have a survival rate of 36 percent.
—The surgical removal and microscopic examination of living
tissue for diagnostic purposes or to follow the course of a disease.
Most commonly the term refers to the collection and analysis of tissue
from a suspected tumor to establish malignancy.
—An immature material from which cells and tissues develop.
—A disease caused by uncontrolled growth of the body's
—Cells that have been altered such that they have lost normal
control mechanisms and are capable of local invasion and spread to other
areas of the body. Often used to describe a cancer.
—A type of cancer that originates from connective tissue such as
bone or muscle.
—Pertaining to the type of tissue that is associated with the
support of an organ.
—Tissues and cells associated with the structures that connect
the renal pelvis to the glomeruli.
Clearly, a child who is undergoing the rigors of treatment for
Wilms' tumor is going to have some very difficult times. Feeling
ill may cause more irritability than usual. Parents will want to consult a
dietician for advice on how to provide the best possible
for their child, who may have a hard time eating due to nausea from
treatment. The child's pediatrician can help provide some
guidelines to help the family understand how the child's
development may be affected by the illness and treatment. Support groups
can be very helpful for families who are facing cancer and cancer
Jaffe, Norman, and Vicky Huff. "Neoplasms of the kidney." In
Nelson Textbook of Pediatrics.
Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2004.
"Wilms' tumor." In
, 8th ed. Edited by Meredith F. Campbell et al. St. Louis, MO: Elsevier,
American Cancer Society.
1515 Clifton Rd. NE, Atlanta, GA 30329. Web site:
March of Dimes Birth Defects Foundation.
1275 Mamaroneck Ave., White Plains, NY 10605. Web site: