This information is about Wilms' tumour in children. It is helpful to read it alongside our general information on children's cancer, which contains more information about cancers in children, their diagnosis and treatment, and the support services available.

About 70 children develop a Wilms' tumour in the UK each year. It most often affects children below the age of five.

Wilms' tumour was named after Dr Max Wilms, who first described it. It is a type of kidney cancer. It is thought to come from very specialised cells in the embryo known as metanephric blastema. These cells are involved in the development of the child's kidneys while they are in the womb. These cells usually disappear at birth, but in many children with Wilms tumour, cells called nephrogenic rests can still be found.

The kidneys are a pair of organs found at the back of the abdomen. They clean the blood to remove excess fluids and waste products. These are then converted into urine.

In most children, the causes of Wilms' tumour are unknown. Very rarely, people who have Wilms' tumour also have other particular conditions present at birth (congenital malformations), such as lack of an iris in the eye (aniridia), abnormalities of the genitals, and a condition where one side of the body is slightly larger than the other (hemihypertrophy). In one in 100 people with Wilms' tumour, another family member will also have Wilms’ tumour.

The most common symptom is a swelling in the abdomen, which is usually painless. Occasionally, the tumour may bleed slightly and this can cause irritation in the area of the kidney, which may be painful. There may be blood in your child’s urine, or their blood pressure may be raised. The child may also have a high temperature (fever), upset stomach, weight loss, or a lack of appetite.

A variety of tests and investigations may be needed to diagnose a Wilms' tumour. Urine and blood samples will be taken to check your child’s kidney function and their general health. An abdominal ultrasound scan and CT scan are often done and this will help the doctors to understand as much as possible about the tumour. Scans of the chest and liver may also be taken to check for any spread of the disease. This is known as staging.

Any tests and investigations that your child needs will be explained to you. Our general information on children’s cancers gives details of what the tests and scans involve.

The 'stage' of a cancer is a term used to describe its size and whether it has spread beyond its original site. Knowing the particular type and the stage of the cancer helps the doctors to decide on the most appropriate treatment.

A commonly used staging system for Wilms' tumours is described below:

• Stage 1 The tumour is only affecting 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, but it is still possible to remove it completely with surgery.
• Stage 3 The tumour has spread beyond the kidney, either because it has burst (before or during the operation), because it has spread to lymph glands (nodes), or because it has not been completely removed by surgery.
• Stage 4 The tumour has spread to other parts of the body such as the lungs, liver, bone or brain. 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.

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 surgery, chemotherapy and sometimes radiotherapy.

All children with Wilms' tumour will have surgery. Initially, this may only involve taking a small sample of cells from the tumour (biopsy) to confirm the diagnosis. The appearance of the Wilms' tumour cells when they are examined under a microscope is important. About one in 10 to one in 20 (5–10%) of Wilms' tumours have an appearance called anaplasia. This is considered a 'higher-risk' tumour and requires a stronger treatment. When tumours are operated on after chemotherapy, a second 'high-risk' category of Wilms' tumour may be identified. This is called a 'blastemal' type (because it contains lots of early cells known as blastemal cells). These cells have survived the pre-surgery chemotherapy.

Other less common types of kidney tumour may occur in children. These are usually only recognised after surgery to obtain a tumour sample. Two cancerous types of tumour are: clear cell sarcoma, and malignant rhabdoid tumour of the kidney. These are treated in a similar way to 'high-risk' Wilms' tumour.

A non-cancerous (benign) tumour that occurs in very young children is known as congenital mesoblastic nephroma. This usually only needs surgery and no other treatment.

If possible, the Wilms' tumour will be removed by surgery, either at diagnosis or following chemotherapy. This usually involves removing all of the kidney (nephrectomy) but occasionally only part of the kidney (partial nephrectomy) is required.

Chemotherapy is usually given after surgery to help reduce the risks of the cancer coming back (recurring). Chemotherapy is the use of anti-cancer (cytotoxic) drugs to destroy cancer cells. It is usually given as injections and drips (infusions) into a vein.

Depending on the stage of the tumour at diagnosis, radiotherapy may also be given to the area of the affected kidney or to the whole abdomen. Radiotherapy treats cancer by using high-energy rays to destroy the cancer cells, while doing as little harm as possible to normal cells.

If the tumour cannot be removed by surgery, chemotherapy and radiotherapy may be given to shrink the tumour. Once the tumour has shrunk, surgery can then often be done to remove it. Further chemotherapy and radiotherapy may also be given. If there are secondary tumours, these may be treated with radiotherapy or chemotherapy.

Bilateral Wilms' tumour affects both kidneys. This cancer occurs in about one in 20 cases. Treatment may involve two operations, a few weeks apart. The aim of the treatment is to remove as much of the cancer as possible, while leaving as much healthy kidney as possible. Chemotherapy is always given. Sometimes radiotherapy is needed as well.

Treatment for Wilms' tumours often causes side effects, and your child’s doctor will discuss this with you before treatment starts. Side effects can include:

• feeling sick (nausea) and being sick (vomiting)
• hair loss
• an increased risk of infection
• bruising and bleeding
• tiredness
• diarrhoea.

Late side effects

A small number of children may develop side effects many years later, because of the treatment they have received for a Wilms' tumour. These include possible reduction in bone growth, infertility, a change in the way the heart and the lungs work, and a slight increase in their risk of developing another cancer in later life. There is more detailed information about these late side effects in the general information on children’s cancers.

Many children have their treatment as part of a clinical research trial. Trials aim to improve our understanding of the best way to treat an illness (usually by comparing the standard treatment with a new or modified version of the standard treatment). Specialist doctors carry out trials for children's cancer. Your child's medical team will talk to you about taking part in a clinical trial (if appropriate) and will answer any questions you may have. Written information is often provided to help explain things. Taking part in a research trial is completely voluntary, and you'll be given plenty of time to decide if it is right for your child.

Most children with Wilms' tumour are cured. If the cancer comes back, it is usually within the first two years.

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 have long-term kidney problems. Your child will have regular follow-ups to check for any recurrence.

If you have specific concerns about your child’s condition and treatment, it is best to discuss them with your child’s doctor, who knows the situation in detail.

As a parent, the fact that your child has cancer is one of the worst situations you can be faced with. You may have many different emotions, such as fear, guilt, sadness, anger and uncertainty. These are all normal reactions, and are part of the process that many parents go through at such a difficult time.

Your child may have a range of powerful emotions throughout their experience of cancer. Our booklet, Peppermint Ward, is a storybook for younger children with cancer. It looks at the issues that they and their family may face, and helps them to explore their feelings.

This section has been compiled using information from a number of reliable sources, including:

• Cancer in Children: Clinical Management (5th ed). Eds PA Voute et al. Oxford University Press, 2005.

For further references, please see the general bibliography.