

Wilms' tumour (kidney cancer in children)

This page tells you about Wilms' tumour, a type of kidney cancer that affects children. There is information about


What are Wilms’ tumours?

Wilms’ tumours, also known as nephroblastomas, are a type of kidney cancer that affects children. Dr Max Wilms wrote the first medical paper about this condition in 1899. This is how it got its name. There is information about the kidneys and what they do in the section about adult kidney cancer.

Kidney cancer in children is rare but this is the most common type they can get. Around 40 children are diagnosed each year in the UK. More than 9 out of 10 kidney cancers (95%) found in children are Wilms' tumours. They are most common in children under 5. They can appear in older children and adults but this is rare.

Wilms’ tumours usually only affect one kidney (unilateral) but in about 7 out of every 100 children (7%) it can affect both (bilateral).

When a baby is growing in the womb, the kidneys develop very early on. Sometimes something goes wrong and some of the cells that should have turned into mature kidney cells don’t. Instead they stay as very immature cells. Often these immature cells mature by the time the child is 3 or 4. But if they don’t, they begin to grow out of control and may develop into a cancer known as a Wilms’ tumour.


Causes of Wilms' tumours

The causes of Wilms’ tumours are unknown. But we have identified several risk factors. These are

Being a girl

Girls are at a slightly higher risk than boys of developing a Wilms' tumour.

Children born with certain abnormalities

Certain genetic mutations that cause birth defects can increase your risk of developing a Wilms' tumour. About 15 out of every 100 children (15%) who develop a Wilms' tumour also have a birth defect.

Most birth defects associated with Wilms' tumours happen in syndromes. A syndrome is a group of symptoms and abnormalities that are present in the same person. Gene mutations affect all body cells. So this explains why children born with one of these syndromes can have several parts of their body affected and not just their kidneys. These syndromes are very rare and tend to have long complicated names. The symptoms they cause help give you a better understanding of them.

The main ones are

WAGR syndrome is a combination of abnormalities in the coloured part of the eye (iris), the genitourinary tract and the brain. The iris is either partially or totally absent (aniridia). There can be defects in the kidneys, urinary system, penis, scrotum, clitoris, testicles or ovaries. And the person may have learning disability.

Beckwith-Wiedemann Syndrome means that children have larger than normal internal organs and often have a very big tongue. Also, one arm or leg may be bigger than the other.

Denys-Drash Syndrome means that babies do not develop a penis, scrotum or testicles and can be mistaken for girls. They also develop damaged kidneys that stop working. A Wilms' tumour can grow in the damaged kidney.

Family history

Between 1 and 2 out of every 100 children (1 to 2%) 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.


Types of Wilms' tumours

There are 2 main types of Wilms’ tumour. The cells in each type look different under a microscope. Doctors call this the histology of the tumour. The 2 types are

  • Wilms' tumour with favourable histology
  • Wilms' tumour with unfavourable histology

Unfavourable histology means that the cells look very large and not like normal kidney cells. The medical term for this is anaplasia. The cancer is less likely to be cured if there are lots of areas of anaplasia. But more than 9 out of 10 Wilms’ tumours (95%) have favourable histology. This means that there is no anaplasia and the chance of cure is high.

Several other very rare types of kidney cancers are found in children. Doctors used to group these as Wilms’ tumours with unfavourable histology but they are now grouped separately. They are treated in the same way as a Wilms' tumour but often more intensively. They are

  • Clear cell sarcoma of the kidney (CCSK)
  • Malignant rhabdoid tumour of the kidney

Symptoms of Wilms' tumours

Most Wilms' tumours are quite large when they are found. They are very often much bigger than the kidney itself. Fortunately, even though they are large, most of them have not spread to other parts of the body. The most common symptom is a painless swelling of the abdomen. Parents may notice this if their child suddenly jumps a nappy size. Other less common symptoms include

  • Bleeding inside the tumour causing pain
  • Blood in the urine – found in between 15 and 20 out of every 100 children (15 to 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)

Treating Wilms’ tumours

The treatment for a Wilms’ tumours depends on the size of the cancer and whether or not it has spread to nearby lymph nodes. The main treatments include surgery, radiotherapy or chemotherapy. 

All children will have surgery to remove the affected kidney. This operation is called a nephrectomy. The surgeon removes the whole kidney with the tissues around it including the adrenal gland and some lymph nodes in the area. The adrenal gland is attached to the kidney. Some tumours are removed using keyhole surgery. For keyhole surgery the surgeon makes a few small cuts in the skin over the kidney rather than one larger wound. They put a tube with a light a eyepiece through one cut and instruments to remove the tumour through the other cuts.

Your child's surgeon will discuss with you which type of surgery is best in their case. 

Sometimes the tumour may be too big to remove, or may have spread to nearby areas or to both kidneys. If this is the case your doctor may give cancer killing drugs (chemotherapy) or use radiotherapy before surgery to shrink the tumour before doing an operation. After surgery, some children may have chemotherapy, radiotherapy or both. This treatment is to kill off any cancer cells left behind.

Because this type of tumour is so rare it is treated in specialist centres. This is usually in a major children's cancer centre. These centres have teams of specialists who know about Wilms’ tumours and the best way to treat them.


Research into Wilms' tumours

There is research taking place looking at different combinations of chemotherapy drugs for Wilms' tumour. And as more children get better from their Wilms' tumour, doctors are studying the long term effects of chemotherapy and radiotherapy treatments.

There is information about these studies on our clinical trials database. Type 'Wilms' into the search box.


Getting support and information

Parents have a lot to think about and are likely to be very worried about getting the best treatment for their child. Feeling frightened about one of your children having cancer is normal. The good news is that Wilms' tumour is curable in more than 9 out of 10 children (90%) diagnosed. Talk to the doctors about any worries that you have. They will understand and will want you to feel comfortable and confident with the treatment and care that your child is getting.

There is information and links to many websites about Wilms’ tumours on the Children’s Cancer Web. A lot of this information is from American websites but there are some UK links.

You can also contact the Cancer Research UK information nurses on freephone 0808 800 4040, from 9am until 5pm, Monday to Friday.

Our page about children's cancer organisations gives details of organisations you can contact for information, help and support. The Children's Cancer and Leukaemia Group (CCLG) have a booklet called A Parent’s Guide to Children’s Cancers – For parents and carers. The booklet gives general information about childhood cancer, treatments and where to get further information and support. It is helpful for parents and grandparents. The CCLG also has factsheets about individual types of children’s cancer and their treatment.

Cancer Research UK has an online forum called Cancer Chat. You may find it helpful to join the forum to

  • Talk to other people whose children or grandchildren have cancer
  • Share your experiences
  • Find information
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Updated: 16 January 2014