What is Wilms tumour?

Wilms tumours are a type of kidney cancer that mainly affect children. They develop from cells called nephroblasts and so are also called nephroblastomas. Dr Max Wilms wrote the first medical paper about this condition. This is how it got its name. 

Kidney cancer in children is rare but Wilms tumour is the most common type. Almost 85 children between the ages of 0 and 14 years are diagnosed with Wilms tumour each year in the UK. They are most common in children under 5. Rarely they can develop in older children and very rarely, in adults.

Wilms tumours usually only affect one kidney (unilateral). But in fewer than 10 out of every 100 children (less than 10%), it can affect both kidneys (bilateral).

The kidneys

The kidneys are part of your urinary system. This system filters water and waste products out of the blood and makes urine. It includes:

  • 2 kidneys
  • 2 ureters
  • bladder
  • urethra
Diagram showing a child's renal system

Inside the kidney, tiny networks of tubes called nephrons filter the blood. As blood passes through the nephrons all unwanted water and waste gets taken away. Chemicals that your body needs are kept and returned to the bloodstream.

Diagram showing exit routes for waste products and a nephron in the kidney

Inside the nephrons, waste products move from the small blood vessels into urine collecting tubes. The urine gathers in an area called the renal pelvis at the centre of each kidney. From here it drains down a tube called the ureter and into the bladder.

There are 2 ureters, one from each kidney. Another tube called the urethra carries the urine from the bladder out of the body.

How Wilms tumours develop

When a baby is growing in the womb, the kidneys develop very early on. Sometimes something goes wrong. This can cause some of the early (immature) cells (or nephroblasts) to not turn into developed (mature) kidney cells. If this happens, they begin to grow out of control and may develop into a cancer known as a Wilms tumour.


The causes of Wilms’ tumours are unknown. We know about some factors that may increase the risk for a very small number of children. Anything that increases your risk of getting a disease is called a risk factor. 

Children born with certain abnormalities

About 5 out of every 100 children (5%) who develop a Wilms tumour also have a birth defect.

Most birth defects associated with Wilms tumours happen in rare syndromes (a group of symptoms and abnormalities that are present in the same person) that affect several parts of the body, not just the kidneys.

WAGR syndrome

WAGR syndrome stands for Wilms tumour, Aniridia, Genitourinary problems and Range of developmental delays. 

Children with WAGR syndrome have abnormalities in the coloured part of the eye (iris) and brain. There can also be defects in the kidneys, penis, scrotum, clitoris, testicles or ovaries. The child may also have a learning disability.

Beckwith-Wiedemann syndrome

Children with Beckwith-Wiedemann syndrome have a growth disorder. They have larger than normal internal organs and often have a very big tongue. These children might have one side of the body or an area such as an arm or leg that is bigger than the other. In the first few days or weeks of life, they might have low blood sugar.

There are also other problems that might occur, but what’s listed above are some of the most common problems.

Denys-Drash Syndrome 

This syndrome affects the kidneys and sexual organs (genitalia). Boy babies do not develop a penis, scrotum or testicles and can be mistaken for girls. They also have damaged kidneys. Girls have normal sexual organs but have problems with their kidneys. A Wilms tumour can grow in the damaged kidney.

A family history of Wilms tumour

About 1 of every 100 children (about 1%) with a Wilms tumour have at least one relative who has had the same type of cancer. These children are at an increased risk of developing a Wilms tumour because they have inherited an abnormal gene from one of their parents.

Screening children at risk of developing Wilms tumour

Your doctors will work out your child’s risk of developing a Wilms tumour. It is important to remember that screening will not prevent your child from getting a Wilms tumour. The aim is to find it early.

The length of time your child has screening for will depend on their risk. Screening varies and happens till your child reaches the age of about 7 years of age. Screening usually involves your child having a regular ultrasound scan. Your doctor will talk more about this with you based on your child’s circumstances.

Staging, types and risk groups

The stage of a cancer tells you how big it is and whether it has spread. Knowing the stage can help your doctor decide on the right treatment. And it can help to predict the outcome after treatment.

Doctors group Wilms tumours in terms of risk. This looks at whether there is a low, medium or high risk of the cancer coming back after treatment. In the UK, doctors usually decide on the risk group after they see how the tumour responds to the initial treatment.

Most tumours are in the low or medium risk group. High risk tumours often have cells that look very large and not like normal kidney cells under a microscope. The medical term for this is anaplasia. The cancer is less likely to be cured if there are lots of areas of anaplasia.

Some Wilms tumours have early kidney cancer cells that chemotherapy can’t get rid of straightaway. These early cells are called blastemal cells. Tumours with lots of blastemal cells remaining after chemotherapy are also put into the high risk group. 

Rare types of kidney cancer

Other rare types of kidney cancers are found in children. Doctors used to group these as Wilms tumours with unfavourable histology Open a glossary item but they are now grouped separately.

They are treated in a similar way to a Wilms' tumour but often more intensively. They are:

  • clear cell sarcoma of the kidney (CCSK)
  • malignant rhabdoid tumour of the kidney
  • mesoblastic nephroma - this is usually seen in very young babies and is usually a non cancerous tumour
  • renal cell carcinoma - this is usually seen in teenagers


Most Wilms tumours are quite large when they are found. Often bigger than the kidney itself. Most of them have not spread to other parts of the body. 

The most common symptom is a painless swelling of the tummy (abdomen). Parents might notice a lump in the tummy when bathing the baby, or if their child suddenly jumps a nappy size. Or, a healthcare worker might notice a swollen tummy when the child is having a routine appointment.

Other less common symptoms include:

  • bleeding inside the tumour causing pain
  • blood in the urine – found in around 20 out of every 100 children (20%) with a Wilms tumour
  • raised blood pressure
  • high temperature (fever)
  • loss of appetite
  • weight loss
  • feeling or being sick
  • shortness of breath and cough (only if the cancer has spread to the lungs)
  • generally feeling unwell
  • looking pale due to a low number of red blood cells (anaemia)
  • being irritable due to their tummy feeling uncomfortable

Remember Wilms tumour is very rare. Having these symptoms doesn’t mean your child has cancer. But it’s important to take them to the GP, so any problems can be looked into.

Referral to a specialist

Your GP should refer your child to a specialist within 48 hours (2 days) if they have any of the following:

  • a lump in the tummy (abdomen)
  • a larger than normal organ in the tummy
  • blood in the urine

This is called an urgent referral.

Diagnosing Wilms tumour

There are a number of tests your doctors might do if they suspect your child has a Wilms tumour.

Last reviewed: 
12 Oct 2020
Next review due: 
12 Oct 2023
  • Children, teenagers, and young adults UK cancer statistics report 2021
    Public Health England (PHE), 2021

  • Childhood cancers – Recognition and referral: Symptoms suggestive of childhood cancers.
    National Institute for Health and Care Excellence (NICE), Lasted updated August 2020

  • Wilms’ tumour: biology, diagnosis and treatment
    E Szychot, J Apps, and K Pritchard-Jones
    Translational Pediatrics, 2014. Volume 3, Issue 1, Pages 12 to 14.

  • BMJ Best Practice
    S Batra and others
    BMJ Publishing Group, Last updated December 2017

  • Pharmacotherapeutic management of Wilms tumour: an update
    R M Oostveen and K Pritchard-Jones
    Pediatric Drugs, 2019. Volume 21, Pages 1 to 13

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact patientinformation@cancer.org.uk with details of the particular issue you are interested in if you need additional references for this information.

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