The cause of Wilms tumor is not known, but some children may have a genetic abnormality that increases their risk of developing this tumor.
Children usually have a lump in the abdomen, and they may also have abdominal pain, fever, poor appetite, nausea, and vomiting.
An imaging test is done to determine the nature and size of the lump.
Treatment involves surgery and chemotherapy and sometimes radiation therapy.
(See also Overview of Childhood Cancer Overview of Childhood Cancer Cancer is rare among children. In 2021 in the United States, an estimated 10,500 children aged birth to 14 years will be diagnosed with cancer and slightly over 1,100 children will die of it... read more .)
Wilms tumor usually develops in children younger than 5 years old, although it occasionally occurs in older children and rarely in adults. Very rarely, it develops before birth and appears in newborns. In about 5% of cases, Wilms tumor occurs simultaneously in both kidneys.
The cause of Wilms tumor is not known, although a lack of certain genes or another genetic abnormality may be involved in some cases. Wilms tumor is more likely to develop in children with certain birth defects, for example, when both irises are missing or when one side of the body grows too much. Problems with the kidneys, genitals, and urinary tract are common also. These defects, as well as intellectual disability, may be caused by a genetic abnormality. However, most children with Wilms tumor have no such recognizable abnormalities.
Symptoms of Wilms Tumor
The first symptom of Wilms tumor is often a painless lump in the abdomen. The abdomen may enlarge, which parents may notice when children suddenly need a larger diaper size. Children may also have abdominal pain, fever, poor appetite, nausea, and vomiting. Blood appears in the urine in some children. Because the kidneys are involved in controlling blood pressure, Wilms tumor may cause high blood pressure High Blood Pressure High blood pressure (hypertension) is persistently high pressure in the arteries. Often no cause for high blood pressure can be identified, but sometimes it occurs as a result of an underlying... read more 
(hypertension).
This cancer can spread to other parts of the body, especially the lungs. If the lungs are involved, children may cough and be short of breath.
Diagnosis of Wilms Tumor
Ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI) of the abdomen
Often surgery to remove the tumor at the time of diagnosis
Wilms tumor is most often detected when parents notice a lump in the child’s abdomen and take their child to a doctor. Or a doctor may feel such a lump during a routine examination. If the doctor suspects Wilms tumor, ultrasonography, CT Computed Tomography (CT) In computed tomography (CT), which used to be called computed axial tomography (CAT), an x-ray source and x-ray detector rotate around a person. In modern scanners, the x-ray detector usually... read more 
, or MRI Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more 
of the abdomen is done to determine the nature and size of the lump. CT or MRI can also help doctors determine whether the tumor has spread to nearby lymph nodes or the liver and determine if the other kidney is affected. The doctor also does CT of the chest to determine whether tumors have spread to the lungs.
Surgery to remove part or all of the kidney (nephrectomy) that contains the tumor is done in most children based on the results of the CT or MRI. Doctors then analyze the tumor to confirm that it is a Wilms tumor. During surgery, doctors also remove nearby lymph nodes in the abdomen and analyze them for cancer cells. Cancer that has spread to the lymph nodes may require different treatment than cancer that has not.
Prognosis for Wilms Tumor
In general, Wilms tumor is very curable. If the tumor is only in the kidney, about 85% to 95% of children are cured. Even if the tumor has spread beyond the kidney, cure rates range from 60% to 90% depending on how abnormal the cancer cells appear during testing. The outcome is usually better in children who
Are younger
Have cancer cells that are less abnormal when the tumor is examined under a microscope
Have a tumor that has not spread
However, there is one type of Wilms tumor (which accounts for less than 5% of cases) that is more resistant to treatment. Children with this type of tumor have a poorer prognosis.
Wilms tumor can return, typically within 2 years of diagnosis. Children whose cancer has returned can still be cured.
Treatment of Wilms Tumor
Surgery and chemotherapy
Sometimes radiation therapy
(See also Cancer Treatment Principles Cancer Treatment Principles Treating cancer is one of the most complex aspects of medical care. It involves a team that encompasses many types of doctors working together (for example, primary care doctors, gynecologists... read more and Surgery for Cancer Surgery for Cancer Surgery is a traditional form of cancer treatment. It is the most effective in eliminating most types of cancer before it has spread to lymph nodes or distant sites (metastasized). Surgery may... read more .)
Doctors treat Wilms tumor by removing the kidney that contains the tumor. During the operation, the other kidney is examined to determine whether it also has a tumor. After surgery, doctors give the child chemotherapy drugs Chemotherapy and Other Systemic Cancer Treatments Systemic treatments are those that have effects throughout the body rather than being applied directly to the cancer. Chemotherapy is a form of systemic treatment that uses drugs to kill cancer... read more —most commonly dactinomycin and vincristine and sometimes doxorubicin. If the cancer has spread significantly, children are also treated with radiation therapy Radiation Therapy for Cancer Radiation is a form of intense energy generated by a radioactive substance, such as cobalt, or by specialized equipment, such as an atomic particle (linear) accelerator. Radiation preferentially... read more .
Rarely the tumor is extremely large and cannot be removed initially or tumors are in both kidneys. In such cases, children are first treated with chemotherapy to shrink the tumor or tumors. Then the tumor or tumors are removed.
More Information
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
American Cancer Society: If Your Child Is Diagnosed With Cancer: A resource for parents and loved ones of a child who has cancer that provides information about how to cope with some of the problems and questions that come up just after a child is diagnosed
