Wilms tumor is a rare kidney cancer that mainly affects children. Also known as nephroblastoma, it's the most common cancer of the kidneys in children. Wilms tumor most often affects children ages 3 to 4. It becomes much less common after age 5, but it can affect older children and even adults.

Wilms tumor mostly occurs in just one kidney. But it can sometimes be in both kidneys at the same time.

Over the years, progress in the diagnosis and treatment of Wilms tumor has greatly improved the prognosis for children with this disease. With treatment, the outlook for most children with Wilms tumor is good.

Symptoms

Symptoms of Wilms tumor vary a lot. Some children don't seem to have any symptoms. But others with Wilms tumor have one or more of these symptoms:

• A mass in the stomach area that can be felt.
• Swelling in the stomach area.
• Pain in the stomach area.

Other symptoms might include:

• Fever.
• Blood in the urine.
• Low red blood cell level, also known as anemia.
• High blood pressure.

When to see a doctor

Make an appointment with your child's health care provider if you see symptoms that worry you. Wilms tumor is rare. So it's likely that something else is causing symptoms. But it's important to check out any concerns.

Causes

It's not clear what causes Wilms tumor.

Cancer begins when cells develop changes in their DNA. Cells' DNA holds the instructions that tell the cells what to do. The changes tell the cells to grow and multiply quickly. The cancer cells live while healthy cells die as part of their natural life cycle. With Wilms tumor, the changes make extra cells in the kidney that form the tumor.

Rarely, DNA changes passed from parents to children can increase the risk of Wilms tumor.

Risk factors

Factors that may increase the risk of Wilms tumor include:

• Being Black. In North America and Europe, Black children have a slightly higher risk of getting Wilms tumor than do children of other races. Asian-American children appear to have a lower risk than children of other races.
• Having a family history of Wilms tumor. Having someone in the family who's had Wilms tumor increases the risk of getting the disease.

Wilms tumor occurs more often in children who have certain conditions present at birth, including:

• Aniridia. In aniridia (an-ih-RID-e-uh), the colored portion of the eye, known as the iris, forms only in part or not at all.
• Hemihypertrophy. Hemihypertrophy (hem-e-hi-PUR-truh-fee) means one side of the body or a part of the body is larger than the other side.

Wilms tumor can occur as part of rare syndromes, including:

• WAGR syndrome. This syndrome includes Wilms tumor, aniridia, genital and urinary system problems, and intellectual disabilities.
• Denys-Drash syndrome. This syndrome includes Wilms tumor, kidney disease and male pseudohermaphroditism (soo-do-her-MAF-roe-dit-iz-um). In male pseudohermaphroditism, a boy's genitals aren't clearly male.
• Beckwith-Wiedemann syndrome. Children with this syndrome tend to be much larger than what is typical, known as macrosomia. This syndrome might cause organs in the stomach area to jut into the base of the umbilical cord, a large tongue, large internal organs and ears that are formed unusually.

Prevention

Wilms tumor can't be prevented.

If a child has any of the conditions that increase the risk for Wilms tumor, a health care provider might suggest doing kidney ultrasounds at times to look for anything unusual in the kidneys. Although this screening can't prevent Wilms tumor, it may help find the disease at an early stage.

Diagnosis

To diagnose Wilms tumor, a health care provider might take a family history and do the following:

• A physical exam. The provider will look for possible signs of Wilms tumor.
• Blood and urine tests. These lab tests can show how well the kidneys are working.
• Imaging tests. Tests that create images of the kidneys help find whether a child has a kidney tumor. Imaging tests may include ultrasound, CT scans or MRI and chest X-rays.

Staging the cancer

After finding Wilms tumor, the health care team might recommend other tests to see if the cancer has spread. This is called the cancer's stage. A chest X-ray or chest CT scan and bone scan can show whether the cancer has spread past the kidneys.

The stage of the cancer helps with deciding treatment. In the United States, the stages for Wilms tumor are:

• Stage 1. The cancer is found only in one kidney. Surgery can remove it all.
• Stage 2. The cancer has spread beyond the kidney, such as to nearby fat or blood vessels. But surgery can still remove it all.
• Stage 3. The cancer has spread beyond the kidneys to nearby small organs that fight infection, also known as lymph nodes. It might also have spread to other places within the abdomen. The cancer cells might spill within the abdomen before or during surgery, or surgery might not be able to remove all the cancer.
• Stage 4. The cancer has spread outside the kidney to other places in the body, such as the lungs, liver, bones or brain.
• Stage 5. Cancer cells are found in both kidneys. The tumor in each kidney is staged by itself.

Treatment

Treatment for Wilms tumor usually involves surgery and chemotherapy. It sometimes includes radiation therapy. Treatments depend on the stage of the cancer. Because this type of cancer is rare, a children's cancer center that has treated this type of cancer might be a good choice.

Surgery

Treatment for Wilms tumor may begin with surgery to remove all or part of a kidney. Surgery also confirms the diagnosis. The tissue removed during surgery is sent to a lab to learn whether it's cancerous and what type of cancer is in the tumor.

Surgery for Wilms tumor may include:

• Removing part of the kidney. Known as a partial nephrectomy, this involves removing the tumor and a small part of the kidney around it. This might be done if the cancer is very small or for a child who has only one working kidney.
• Removing the kidney and surrounding tissue. Known as a radical nephrectomy, this type of surgery also involves removing nearby lymph nodes, part of the ureter and sometimes the adrenal gland. The kidney that's left can take on the work of both kidneys.
• Removing all or part of both kidneys. If the cancer affects both kidneys, surgery involves removing as much cancer as possible from both. Sometimes, this means removing both kidneys. The child would then need kidney dialysis or a kidney transplant.

Chemotherapy

Chemotherapy uses strong medicines to kill cancer cells throughout the body. Treatment for Wilms tumor usually involves using more than one medicine to kill cancer cells. The medicine is given through a vein.

Side effects of chemotherapy depend on the medicines used. Common side effects include nausea, vomiting, loss of appetite, hair loss and higher risk of infections. Ask your child's health care team what side effects might happen during treatment. Ask if there might be long-term problems as a result of treatment.

If given before surgery, chemotherapy can shrink tumors and make them easier to remove. After surgery, it can kill cancer cells that are left in the body. Chemotherapy may also be an option for children whose cancers are too far along to be removed completely with surgery.

For children who have cancer in both kidneys, chemotherapy is given before surgery. This may make it more likely that one kidney might be saved.

Radiation therapy

Some children might have radiation therapy. Radiation therapy uses high-powered energy beams to kill cancer cells. The energy can come from X-rays, protons and other sources.

During radiation therapy, the child is placed on a table. A large machine moves around the child, pointing energy beams at the cancer. Possible side effects include nausea, diarrhea, tiredness and sunburn-like skin irritation.

Some children will have radiation therapy after surgery to kill any cancer cells that are left. It also might be used to control cancer that has spread to other areas of the body. Ask if there might be long-term problems as a result of radiation therapy.

Coping and support

Here are some suggestions to help you guide your family through cancer treatment.

At the hospital

When your child has medical appointments or stays in the hospital:

• Bring a favorite toy or book to office or clinic visits, to keep your child busy while waiting.
• Stay with your child during a test or treatment, if possible. Describe what will happen using words the child knows.
• Include play time in your child's schedule. Major hospitals usually have a playroom for children being treated. Often playroom staff members have training in child development, recreation, psychology or social work. For children who must stay in their rooms, a child life specialist or recreational therapist might be able to visit.
• Ask for support from clinic or hospital staff members. Look for organizations for parents of children with cancer. Parents who have been through this can provide support, hope and good advice. Ask your child's health care team about local support groups.

At home

After leaving the hospital:

• Monitor your child's energy level outside of the hospital. If your child feels well enough, gently encourage taking part in regular activities. Also make time for rest, especially after chemotherapy or radiation.
• Keep a daily record of your child's body temperature, energy level, sleep, medicines used and side effects. Share this information with your child's health care provider.
• Plan a typical diet unless your child's provider suggests otherwise. Make favorite foods. Chemotherapy can affect wanting to eat. Increase fluids.
• Encourage mouth care. A mouth rinse can be helpful for sores or areas that are bleeding. Use lip balm to soothe cracked lips. Ideally, your child should have needed dental care before treatment begins. Afterward check with your child's provider before scheduling visits to the dentist.
• Check with the provider before vaccinations. Cancer treatment affects the immune system.
• Talk with your other children about the illness. Tell them about changes they might see in the child who has cancer, such as hair loss and low energy. Listen to their concerns.

Preparing for an appointment

If your child is diagnosed with Wilms tumor, you may be referred to specialists. This might be a doctor who treats cancer, which is called an oncologist, or a surgeon who specializes in kidney surgery, which is called a urologist.

What you can do

To prepare for the appointment:

• Make a list of all medicines, vitamins, herbs, oils and other supplements that your child is taking, including doses.
• Ask a family member or friend to come with you to help you remember the information you get during the appointment.
• Write a list of questions to ask your child's health care provider.

For Wilms tumor, some questions to ask include:

• What tests does my child need?
• What stage is my child's cancer?
• What treatments are available, and which do you recommend?
• What types of side effects can these treatments cause?
• Will I need to restrict my child's activity or change the diet during treatment?
• What's my child's outlook?
• What is the likelihood that the cancer will come back?
• Are there brochures or other printed material I can have? What websites do you recommend?

Don't hesitate to ask other questions you have.

What to expect from your doctor

Your child's health care provider is likely to ask you a questions, such as:

• When did you notice your child's symptoms?
• Is there a history of cancer, including childhood cancer, in your family?
• Does your child have any family history of birth defects, especially of the genitals or urinary tract?