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Learning About Wilms Tumor

Location of kidneys and bladder in a child

What is Wilms tumour?

Wilms tumour is a tumour (growth of abnormal cells) in the kidney. It's the most common type of kidney cancer in children. It is most common in children younger than 5. In many cases, Wilms can be treated and cured.

Wilms is usually in one kidney (unilateral), but it can be in both (bilateral).

The cancer cells can spread to nearby lymph nodes. Or they may spread to other parts of the body, most often the lungs or liver.

What causes it?

Experts think that Wilms tumour may be caused by problems in the way the kidney develops. Or it may be related to gene changes. Most children who get Wilms have no other health problems.

Some children are born with genetic conditions that increase the chance of having a Wilms tumour. In very rare cases, Wilms may run in families.

What are the symptoms?

Symptoms of Wilms tumour include:

  • A mass in the belly. You or your child's doctor might find a lump.
  • Blood in your child's urine.
  • Belly pain.
  • Fever.
  • High blood pressure.

How is it diagnosed?

The doctor will ask about your child's past health. He or she will do a physical exam.

Your child may have several imaging tests. An ultrasound test may be the first test used. CT or MRI scans can show the size of the tumour and if it's spread. Your child may have other tests such as:

  • A urine test.
  • Blood tests.
  • A biopsy. A sample of the tumour is sent to a lab so that it can be looked at under a microscope. It can show if something is cancer and what type.
  • Genetic tests.

How is it treated?

Most of the time, a doctor will use surgery to remove the kidney with the tumour in it.

And in most cases, chemotherapy (chemo) will be used to destroy any cancer cells that are left. Chemo is medicine that destroys cancer cells. Your child may start chemo even before the tumour is removed.

Radiation therapy may be used for tumours that have spread or that look like they might spread. It uses high-energy rays, such as X-rays. The rays destroy cancer cells and shrink tumours in the body.

Ask your doctor about having your child take part in a clinical trial. A clinical trial is a study of a new or different way to treat cancer. People in clinical trials get the latest treatments for their cancer and are closely watched. Visit for more information about clinical trials in Canada, or call the Canadian Cancer Society's information service at 1-888-939-3333.

You can also visit the U.S. National Cancer Institute's clinical trials website at This site includes studies conducted in Canada.

What are the stages?

After the tumour is removed, the doctor will talk with you about the stage of your child's cancer. There are 5 stages. Stage 1 means the tumour was still in the kidney and came out in one piece. Stages 2 to 4 mean the cancer has spread beyond the kidneys or to another organ, like the lungs. Stage 5 means that the cancer is in both kidneys.

The stage also helps doctors plan treatment after biopsy or surgery.

What are some things to think about?

  • Some tumours are aggressive and need treatment right away. But most cancer grows slowly enough that you can take a little time to find out more about your child's cancer as you decide about treatment.
  • Talk to your child. Answer all of your child's questions honestly. If you don't know the answers, help your child find out.
  • Ask any questions you might have. You can talk to the doctor, nurses, counsellors, and other advisors.
  • Talk to family, friends, and supporters. Get the kinds of help you need.
  • Think about getting a second opinion from another doctor. Before your child starts major treatment, it's a good idea to check with another doctor about the type of cancer your child has and what stage it is. Your child's doctor can recommend someone for a second opinion.

For further information see Children’s Oncology Group Wilms Tumor.

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