Wilms tumor is a cancerous tumor that starts in the cells of the kidney. It's the most common type of kidney cancer in children. It's often found by the time a child is age 5. The tumor can be very large before it's found. And it may spread (metastasize) to other body tissues. The most common site for Wilms tumor to spread to is the lungs. But it may also spread to the liver, lymph nodes, other kidney, brain, and bones.

Most cases of Wilms tumor occur by chance with no clear cause. Defects in genes affect the growth of kidney cells. But it's not common for Wilms tumor to run in families.

A small number of children with Wilms tumor also have a syndrome caused by abnormal genes, such as:

• WAGR
• Denys-Drash
• Beckwith-Wiedemann

Some birth defects may increase the chance of Wilms tumor. For example, a child with defects of the penis or testicle may be more at risk. Talk with your child's doctor if you want more information about these conditions.

Symptoms can be different for each child. They can include:

• A lump in the belly (abdomen)
• Belly swelling
• Pain in the belly, but some children have no pain
• Blood in the urine
• Low red blood cell count (anemia)
• Fever
• High blood pressure (hypertension)

Many of these symptoms may be caused by other health problems. It's very important to see your child's doctor right away if you notice these symptoms. Only a doctor can tell if your child has cancer.

If your child's doctor thinks your child might have Wilms tumor, certain exams and tests will be needed to be sure. Your child's doctor will ask about your child's health history and symptoms. They'll examine your child. Your child may have tests, such as:

• Abdominal ultrasound. This test uses sound waves and a computer to create pictures of blood vessels, tissues, and organs. It can show the kidney, the tumor, and blood vessels of the kidney. It can also help show if there are any tumors in the other kidney or other parts of the belly (abdomen).
• Abdominal CT scan. This test uses a series of X-rays and a computer to make detailed images of the belly (abdomen). CT scans are much more detailed than standard X-rays.
• MRI. This test uses magnets, radio waves, and a computer to make detailed images of the body. MRI can show if cancer has spread to other parts of the body (metastasized). It can also show if there are cancer cells in the lymph nodes or other nearby organs.
• Chest X-ray. An X-ray is done with a small amount of radiation. It can show if the cancer has spread to the lungs.
• Blood and urine tests. These can check how well the kidneys and liver are working and check overall health.
• Biopsy. A small piece of tissue is removed and checked with a microscope for cancer cells. Samples of the tumor, nearby lymph nodes, and other tissue may be taken. A biopsy can also show the type of tumor. A biopsy of kidney tissue may not be done with some tumors.

Most children with Wilms tumor can be cured. Treatment will depend on the size and location of the tumor and other factors. Your child will be treated by specialists with experience in treating Wilms tumor. They may include a pediatric surgeon and a pediatric cancer specialist (oncologist). The cancer can be treated with any of the below:

• Surgery. This is done to take out the affected kidney (nephrectomy). Removing only part of the kidney isn't advised for most children. Samples of the kidney that's removed are studied. Samples of nearby lymph nodes may also be taken and checked for signs of cancer.
• Chemotherapy. These are medicines that kill cancer cells. They're used to destroy cancer cells before or after surgery. They're also used to treat cancer that has spread or grows back.
• Radiation therapy. These are high-energy X-rays or other types of radiation. Radiation is used to kill cancer cells or stop them from growing. It may be used to treat cancer that has spread or grows back.
• Supportive care. Cancer treatment can cause side effects. Medicines and other treatments can be used to help ease side effects, such as pain, fever, infection, and nausea and vomiting.
• Clinical trials. Ask your child's doctor if there are any new treatments being tested that may work well for your child.

Your child will need follow-up care during and after treatment to:

• Check on your child's response to the treatment.
• Manage the side effects of treatment.
• Look for returning or spreading cancer.

Some treatments may be hard on your child, but they increase the chance of your child living a long time. Discuss the side effects of treatment with your child's doctor.

With any cancer, how well a child is expected to recover (prognosis) varies. Keep in mind:

• Getting medical treatment right away is important for the best outcomes.
• Ongoing follow-up care during and after treatment is needed.
• New treatments are being tested to improve outcomes and to reduce side effects.

You can ask your child's doctor about survival rates and what you might expect. But remember that statistics are based on large groups of people. They can't be used to say what will happen to your child.

Possible complications can include:

• Side effects of chemotherapy or radiation therapy, such as heart failure or growth of a new type of cancer
• Problems from surgery, such as bleeding or infection
• Problems having children in the future
• Cancer that grows back or spreads
• Death

Your child's care team will review what complications you need to think about based on your child's specific treatment plan.

You can help your child manage their treatment in many ways. For example:

• Learn as much as you can about Wilms tumor. This can help you make the best decisions for your child.
• Get emotional support for your child. Finding a counselor or child support group can help.
• Get emotional support for yourself and other family members, especially siblings.
• Take your child to all appointments and treatment visits.
• Your child may have trouble eating. A dietitian may be able to help.
• Your child may be very tired. They'll need to balance rest and activity. Encourage your child to get some exercise. This is good for overall health. And it may help to reduce tiredness.

Your child may need to:

• Be checked for Wilms tumor if they have a condition that increases the chance of developing Wilms tumor
• Have genetic testing and counseling

If needed, consider using the provisions under the Family and Medical Leave Act. This federal law gives you the right to take up to 12 work weeks of unpaid leave to care for a sick family member. For eligible employees, health insurance must continue. When you go back to work, you'll be given your previous position or an equivalent job. For information, see the U.S. Department of Labor website.

Contact the doctor if your child has:

• Symptoms that get worse.
• New symptoms.
• Side effects from treatment.

Ask the doctor about any problems or changes you should watch for and what you should do if you notice them.

• Wilms tumor is cancer that starts in the kidney cells.
• It's most often found in children by age 5.
• It may not cause any symptoms and may not be diagnosed until it's large.
• Surgery, chemotherapy, and radiation therapy may be used to treat Wilms tumor.
• Most children with Wilms tumor can be cured with treatment.

Tips to help you get the most from a visit to your child's doctor:

• Know the reason for the visit and what you want to happen.
• Before your visit, write down questions you want answered.
• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you for your child.
• Know why a new medicine or treatment is prescribed and how it will help your child. Also know what the side effects are.
• Ask if your child's condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if your child doesn't take the medicine or have the test or procedure.
• If your child has a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your child's doctor after office hours and on weekends and holidays. This is important if your child becomes ill and you have questions or need advice.