Wilms' tumor is the most common form of kidney cancer in children, accounting for 6 to 8 percent of all childhood cancers. About 500 new cases are diagnosed in the USA per year. The exact cause is not known, although it is thought that in 10-15% of affected individuals, one or more mutated genes create a predisposition to Wilms' tumor.
Typically, this disease first appears when the affected child is about three years old. Wilms' tumor can often be treated successfully, depending on the stage of the tumor at detection and the age and general health of the child.
In the early stages, Wilms’ tumor usually has no apparent symptoms. It may remain undetected until a parent or pediatrician notices a mass (lump) in the child’s abdomen. Later signs may include blood in the urine, low-grade fever, loss of appetite, paleness, weight loss, and lethargy. There may be intermittent stomach pain, nausea and vomiting, as well as general discomfort (malaise). These symptoms could be due to a variety of other disorders, but parents who observe such symptoms should consult a doctor promptly.
For reasons that have to do with the genetics of Wilms’ tumor, children born with an undeveloped or underdeveloped iris (aniridia), the membrane that controls for the amount light entering the eye and for the color of eye, may be predisposed to Wilms’ tumor. The same is true of children born with one side of the body considerably larger than the other (hemihypertrophy). The diagnosis should also be suspected if the newborn presents with the opening of the urethra on the underside of the penis or if one or both testicles are undescended.
The exact causes of Wilms’ tumor are not known at this time, but both genetic and non-genetic factors are of interest.
All cases of Wilms’ tumor involve a “bunch” or “bundle” of leftover embryonic kidney cells (called nephrogenic rests) that, for some reason, did not develop at the same time as the other embryonic cells.
The location of these embryonic cells in the kidney appears to have an effect on the course of the disease. For example, if the embryonic cells are located within the kidney (intralobar), it is almost inevitable that the tumor involves only one kidney. However, if the embryonic cells are located on the edge of the kidney (perilobar), it is more likely that the tumor will invade both kidneys.
The genetic mutations associated with Wilms’ tumor appear to be random (sporadic) rather than inherited from parent to child (familial) in most cases. Only a very small percentage of cases of Wilms’ tumors are thought to be familial.
Wilms’ tumor accounts for about six to eight percent of all childhood cancers in the USA. The disorder affects one child in about 100,000 in the United States under the age of 15, so that about 450-500 new cases are seen each year. The onset of Wilms’ tumor occurs mainly in children under the age of seven, with most cases developing between the ages of one and four years of age.
There are slightly fewer males than females among children in whom the disorder affects only one kidney. Significantly more females than males have the bilateral disease (both kidneys are affected).
The investigation of a suspected case of Wilms' tumor usually begins with an ultrasound scan that offers a wide-angle view of the abdominal organs and usually picks up any anomalies that require further investigation. CAT scans of the chest, abdomen and pelvis usually follow in order that suspected tumors and/or tumor cells that have spread from the original site (metastasized) may be better visualized.
Treatment will be determined by the condition (staging) of the tumor. Methods of staging have been developed by the National Wilms' Tumor Study Group (NWTSG).
Staging and Treatment
Stage I. The tumor is limited to the kidney without spreading to other organs, and it has been removed completely. Stage I tumors make up about 40% of all diagnosed Wilms' tumors.
Stage II. Examination of the tumor cells (histology) is favorable, but the tumor has spread to areas around the kidney. Surgical removal is followed by chemotherapy or both radiation therapy and chemotherapy. Stage II tumors make up about 23% of all diagnosed Wilms' tumors.
Stage III. The tumor has spread to areas around the kidney including blood vessels and lymph nodes and/or other organs, making it impossible to remove all of the tumor tissue by surgery. Treatment consists of surgery followed by both radiation therapy and chemotherapy. If the tumor has grown so large that surgical removal is too risky, chemotherapy to reduce the size or bulk of the tumor tissue is tried. Stage III tumors also make up about 23% of all diagnosed Wilms' tumors.
Stage IV. The tumor has spread to organs distant from the kidney, such as lungs, liver, bone and brain. Stage IV patients are treated aggressively by surgical, radiological and chemotherapeutic means. Stage IV tumors make up about 10% of all diagnosed Wilms' tumors.
Stage V. In this stage, tumors are found in both kidneys, each of which is staged separately. Such tumors make up about 5% of all diagnosed Wilms' tumors.
Children treated for Wilms' tumor are usually considered cured if they survive for two years without any sign that the disease has returned. The small number of children with aggressive cell types, or with widespread disease at the time of diagnosis have a poorer outlook, but many of these patients are curable with intensive therapy.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.
For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:
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For information about clinical trials sponsored by private sources, contact:
The National Wilms’ Tumor Study Late Effects, sponsored by Emory University, is being conducted to serve as a resource for Wilms’ tumor patients and their families. Information is being collected from as many participants as possible to determine whether they or their offspring might be at risk for any adverse medical conditions. For information, contact Dollicia David at (404) 785-3633 or Dollicia.David@choa.org.
St. Jude’s Children’s Research Hospital is studying ways to improve the outcome for children with recurrent Wilms’ tumor. A drug called topotecan has shown promising results in previous studies to treat children with other types of cancer. Now, research is being conducted to determine whether this drug may be an effective treatment for children with Wilms’ tumor. For information, contact Jeffrey S. Dome, MD, at (866) 278-5833 or firstname.lastname@example.org.
The National Wilms’ Tumor Study (NWTS) was conducted by a national consortium of hospitals and clinics for the purpose of carrying out controlled clinical trials of new treatments for Wilms’ tumor. Findings of this study are the basis for treatment standards for Wilms’ tumor patients in the United States.
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