Around 90 children are diagnosed with renal tumours every year in the UK. Ninety per cent of these cases are Wilms' tumour (also known as nephroblastoma).
Rarer types of renal tumours are rhabdoid renal tumour, clear cell sarcoma of the kidney and renal carcinoma.
About Wilms' tumour
Wilms' tumour is a type of embryonal tumour, developing from the immature cells from which the kidneys develop. It is thought these cells do not mature normally, instead they remain present in a child’s kidney after birth, then they start to grow out of control, forming a jumbled mass of small immature cells.
Wilms' tumour usually only affects one kidney (unilateral) but, in rare cases, can affect both (bilateral).
Wilms' tumour is one of the most common types of childhood cancer, affecting around 80 children a year in the UK.
As with other embryonal tumours, Wilms' tumour predominantly affects children under the age of five years; the peak incidence is between one and three years of age.
Unilateral tumours occur equally often in boys and girls, but girls are twice as likely to be diagnosed with bilateral tumours.
Although the causes of Wilms' tumour are unknown, some people who develop it have abnormal genes or congenital malformations. Up to one in six children diagnosed with Wilms' tumour also have a malformation syndrome, such as WAGR syndrome, Denys–Drash syndrome or Beckwith-Weidemann syndrome - the highest proportion recorded for any childhood malignancy.
In one in 100 cases, another family member will also have Wilms' tumour.
Most children with Wilms' tumour can be cured, with 90 per cent of patients surviving to five years.
Survival is better for children with unilateral Wilms' tumour than for those with bilateral disease.
Children with other types of renal tumour have a worse prognosis. Rhabdoid renal tumour, whilst rare, unfortunately has few survivors.
The most common symptom of a renal tumour is a swelling in the abdomen, which is usually painless.
Sometimes there may be blood in the child’s urine, or their blood pressure may be raised. The child may also have a fever, upset stomach, weight loss or lack of appetite.
A variety of tests and investigations will need to be carried out before a renal tumour is diagnosed. Urine and blood samples will be taken to check kidney function. An abdominal ultrasound scan and CT scan are often done. Scans of the chest and liver may be taken to check for any spread of the disease.
A biopsy will be taken to provide further information about the tumour. Around five per cent of Wilms' tumours have ‘unfavourable’ histology, characterised by ‘anaplastic’ cells that are harder to eradicate.
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 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 the lymph glands, or because it has not been completely removed by surgery.
Stage 4 - the tumour has spread (metastasized) to other parts of the body such as the lungs or liver.
Stage 5 - there are tumours in both kidneys (bilateral Wilms' tumour).
Treatment will depend on a number of facts including the histology of the tumour (how the cells appear under the microscope) as well as the stage of the disease.
If possible the tumour will be removed by surgery, either at diagnosis or following a course of chemotherapy to shrink the tumour. Sometimes radiotherapy may be used to shrink the tumour.
Surgery usually involves removing the whole kidney (nephrectomy) but occasionally only part of the kidney needs to be removed (partial nephrectomy). Examination of the excised tumour will provide doctors with further information about the nature of the tumour and will determine what further treatment is required.
Most tumours are ‘standard risk’. Some are ‘low risk’ and require less additional treatment than the standard risk tumours. Two types of Wilms' tumour – anaplastic and blastemal – are ‘high risk’ and require more intensive treatment.
Chemotherapy is usually given after the surgery to reduce the risk of the cancer returning. Depending on the stage of the tumour, radiotherapy may also be used.
In children with bilateral disease, the aim of surgery is to remove as much of the cancer as possible, while leaving as much healthy kidney as possible. Chemotherapy will always be given and sometimes radiotherapy will also be used.
Read more: Commonly used terms in treatment
Side effects and complications of treatment
Treatment often causes side effects and these will be discussed with you before treatment starts.
The possible side effects of chemotherapy depend upon the drugs used but may include:
- nausea and vomiting
- hair loss
- reduced resistance to infection
- bruising and bleeding
These problems are all temporary and can be minimised with good supportive care.
Read more: Side effects of treatment
The child will have regular follow-ups to check for any recurrence of the cancer and for any problems that may arise as a result of the treatment they were given (late effects).
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.
A small number of children may develop adverse effects years later because of the treatment they received for a renal tumour. These include possible reduction in bone growth, infertility, problems with heart and lung function and a small increase in risk of developing another cancer. Abdominal radiation in Wilms' tumour patients has been linked with problems in later pregnancies for girls.
If the tumour comes back after initial treatment, this is known as recurrent cancer, or relapse. Most children with renal tumours are cured. If the cancer comes back, it is usually within the first two years.
Read more: Long-term and late effects of treatment
Many children have their treatment as part of a clinical trial.
Trials aim to improve understanding of the best way to treat the cancer, usually by comparing the standard treatment with a new or modified version.
If appropriate, the child’s medical team will discuss participation in a relevant trial. Participation is optional but may offer the opportunity to receive new treatments.
Children with Cancer UK is funding an important project at the Institute of Child Health which could help to improve treatments for Wilms' tumour.
Read more: Molecular evolution of Wilms' tumour
More detailed information about Wilms' tumour and its treatment is available from Macmillan Cancer Support