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A Wilms' tumour is a type of kidney cancer that usually affects young children. Wilms' tumours can appear in older children and adults but this is very rare. A Wilms' tumour is also known as a nephroblastoma

Wilm's tumour is the most common type of kidney cancer in children but is very rare. About 80 children are diagnosed with a Wilms' tumour each year in the UK. The most common symptom is a swollen tummy (abdomen).

The treatment for Wilms' tumour usually includes surgery and may also include chemotherapy and radiotherapy. The outcome (prognosis) for Wilms' tumour is usually very good for all children with a Wilms' tumour. Most children diagnosed with Wilms' tumour will survive long-term.

A Wilms' tumour is a type of kidney cancer that usually affects children. It is named after Dr Max Wilms, who wrote the first medical paper about Wilms' tumour in 1899.

A Wilms' tumour is thought to come from very specialised cells that are involved in the development of a baby's kidneys while they are still in the womb. The specialised cells usually develop into normal kidney cells. Sometimes something goes wrong and some of the cells stay as very undeveloped (immature) cells. These cells may grow out of control and develop into a Wilms' tumour.

Wilms' tumours are often divided into two main groups. The cells in each group look very different when looked at under a microscope. The appearance of cells under the microscope is called histology. The two types are:

  • Wilms' tumour with favourable histology. Most Wilms' tumours have favourable histology. This means that the cells have some similar features to normal kidney cells. Wilms' tumours with favourable histology have an excellent chance of being cured with treatment.
  • Wilms' tumour with unfavourable histology. Unfavourable histology means that the cells look very large and very different to normal kidney cells. This is called anaplasia. The cancer is less likely to be cured if there are lots of cells with anaplasia.

There are several other very rare types of kidney cancers that may occur in children. These include clear cell sarcoma of the kidney and malignant rhabdoid tumour of the kidney. Congenital mesoblastic nephroma is a non-cancerous (benign) tumour that occurs in very young children.

See separate leaflet called Cancer - A General Overview for more general information about cancer

Wilm's tumour is the most common type of kidney cancer in children but is very rare. About 80 children are diagnosed with a Wilms' tumour each year in the UK. Children with a Wilms' tumour are usually aged under 5 years. Wilms' tumours can also appear in older children and adults but this is very rare.

Wilms' tumours usually only affect one kidney (unilateral). However, Wilms' tumours can affect both kidneys (bilateral) in about 1 out of every 20 children who are diagnosed with Wilms' tumour.

In most children, the causes of Wilms' tumour are unknown. In about 1 in 100 children with Wilms' tumour, another family member will also have Wilms' tumour. This is because these children have inherited an abnormal gene from one of their parents. The abnormal gene increases the risk of Wilms' tumour.

Very rarely, people who develop Wilms' tumour have other specific conditions which are present at birth (congenital malformations). These include a lack of an iris at the front of the eye (aniridia). The iris is the coloured area surrounding the black pupil at the front of the eye. Wilms' tumours may also be associated with a condition where one side of the body is slightly larger than the other (hemihypertrophy).

There is also an increased risk of a Wilms' tumour for children with certain other conditions, such as:

  • WAGR syndrome. This syndrome includes the iris either partly or totally missing (aniridia). There can be defects in the kidneys, urinary system and genitals. Someone with WAGR may also have learning disability.
  • Beckwith-Wiedemann syndrome. This causes the internal body organs to be larger than normal. The tongue is often very big and one arm or leg may be bigger than the other.
  • Denys-Drash syndrome. Affected boy babies do not develop normal genitals and can be mistaken for girls. They may also have damaged kidneys as well as a Wilms' tumour.

The most common symptom is a swollen tummy (abdomen). There is usually no pain but the tumour may become painful if it bleeds. The lump in the tummy may be very large and easy to feel. Other symptoms may include:

  • Blood in the wee (urine).
  • High temperature (fever).
  • Upset stomach: loss of appetitie and either feeling sick or being sick (vomiting).
  • Losing weight.
  • Having no appetite.

A variety of tests and investigations may be needed to diagnose a Wilms' tumour. An abdominal ultrasound scan is usually the first thing that is done. This will be followed by an MRI scan and/or a CT scan of the tummy (abdomen) and chest. These scans help to show exactly where the tumour is and whether it has spread to other parts of the body.

Other tests will include blood tests to see how well the kidneys are working (kidney function tests) and to test for anaemia.

A biopsy of the tumour is often needed so that the cells of the tumour can be examined under the microscope. This helps to confirm the diagnosis and which treatments would be most effective for treatment.

The stage of a cancer is used to describe the size of the cancer and whether it has spread to other parts of the body. This helps doctors to decide on the best treatment.

The staging system often used for Wilms' tumours is as follows:

  • Stage 1. The tumour only affects the kidney and has not begun to spread. It can be completely removed with surgery.
  • Stage 2. The tumour has begun to spread beyond the kidney to nearby structures. However it is still possible to remove the tumour completely with surgery.
  • Stage 3. The tumour has spread beyond the kidney. The tumour may have spread to nearby sites such as local lymph glands (nodes), or cannot be completely removed by surgery.
  • Stage 4. The tumour has spread to other parts of the body such as the lungs or liver. The tumours in other parts of the body are known as metastases.
  • Stage 5. There are tumours in both kidneys (bilateral Wilms' tumour).

If the tumour comes back after initial treatment, this is known as recurrent cancer or relapse.

After examining the whole tumour under the microscope, Wilms' tumours can be divided into a number of risk groups. The treatment following surgery will depend on these risk groups. The three main risk groups are known as low risk, intermediate risk and high risk.

Most Wilms' tumours are in the 'intermediate-risk' group. So-called 'low-risk' tumours require less treatment after surgery than intermediate-risk tumours. 'High-risk' tumours need more treatment after surgery than 'intermediate-risk' tumours. The 'intermediate-risk' group is sometimes called the 'standard-risk' group.

If there is any concern that your child may have a Wilms' tumour then they should be seen urgently by a specialist. One the diagnosis has been made, treatment is planned by specialists in children's tumours and cancers.

The treatment will depend on a number of factors, including how the cells appear under the microscope (histology) and the stage of the tumour. Treatment usually includes an operation (surgery) and may also include chemotherapy and radiotherapy.


All children with Wilms' tumour will have surgery. Apart from very young children (under 6 months), most children will receive chemotherapy before having a bigger operation to remove the whole tumour. Babies aged under 6 months usually have surgery straightaway without receiving any chemotherapy treatment before the operation.

The aim of surgery is to remove as much of the cancer as possible. Surgery may involve removing the whole of the affected kidney (nephrectomy). However, as much normal healthy kidney as possible is left in place (preserved), especially for bilateral Wilms' tumours.


Chemotherapy is often given before surgery. This is neoadjuvant chemotherapy. Further chemotherapy may be needed after surgery, especially for 'high-risk' Wilms' tumours, This is called adjuvant chemotherapy. Adjuvant chemotherapy helps to reduce the risk of the cancer coming back.


Not all children with Wilms' tumour need radiotherapy. Radiotherapy may occasionally be used to shrink tumours that are too large to remove by surgery. Radiotherapy can also be used when tumours have spread elsewhere in the body.


After treatment for Wilms' tumour your child will need regular check-ups with a specialist to look for any return of cancer or for problems following treatment.

The outcome for Wilms' tumour is very good for all children, whatever their tumour stage. With treatment, 9 out of every 10 children diagnosed with Wilms' tumour survive long-term. Most of the children with cancer that has spread to other parts of the body (metastatic disease) also survive long-term.

When one kidney is removed, the other will be able to work normally and can take over the work of the other kidney. Very few children with Wilms' tumour have long-term kidney problems.

If the cancer comes back it is usually within the first two years. If this happens, further treatment can be given. This may include further surgery, radiotherapy and sometimes high-dose chemotherapy.

There is a slight increased risk of survivors of Wilms' tumour developing another cancer. Examples of these 'second tumours' include bone and soft tissue sarcomas, breast cancer, leukaemia, lymphoma, bowel (gastrointestinal) tumours and skin cancer (melanoma).

Other late side-effects may also occur many years later. These include effects on bone growth. Infertility is also a possible late side-effect many years after successful treatment for Wilms' tumour.


Further reading and references