What is Wilms tumour?

Wilms tumours are a type of kidney cancer that mainly affect children. Wilms tumours are also called nephroblastomas. They develop from cells called nephroblasts. 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. About 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 years. 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

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.

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 early (immature) cells (or nephroblasts) to not develop into mature kidney cells. If this happens, the cells begin to grow out of control and may develop into a cancer known as a Wilms tumour.

Causes of 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. 

Doctors have found that some Wilms tumours have changes in specific genes . But it’s not clear why these changes happen. Doctors are likely to find changes in different genes in the future. This may help them understand more about the causes of Wilms tumour.

Children born with certain abnormalities

About 8 out of every 100 children (about 8%) who develop a Wilms tumour also have other conditions that may be present at birth. 

The conditions associated with Wilms tumours happen in rare syndromes. A syndrome is a group of symptoms and abnormalities that are present in the same person. They 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 in the brain. There can also be defects in the kidneys, penis, scrotum , 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 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.

Other problems might occur. We have listed above 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. 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 2 in every 100 children (about 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.

Screening children at risk of developing Wilms tumour

Screening aims to find a cancer early before symptoms develop. 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 is screened depends on their risk. Screening varies and may continue until your child reaches the age of 7 years. 

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.
 

Symptoms of Wilms tumour

Most Wilms tumours are quite large when they are found. Most 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:

• blood in their wee (urine)
• pain caused by bleeding inside the tumour
• loss of appetite
• raised blood pressure
• high temperature (fever)
• weight loss
• constipation
• generally feeling unwell
• being irritable due to their tummy feeling uncomfortable
• shortness of breath and cough (usually if the cancer has spread to the lungs)

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.

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.

Wilms tumour risk groups

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 Wilms tumours are in the low or medium risk group.

There are 2 types high risk Wilms tumours:

• anaplastic and
• blastemal

Anaplastic cells often have cells that look very large and not like normal kidney cells under a microscope.

Some Wilms tumours have early kidney cancer cells that chemotherapy can’t get rid of straightaway. These early cells are called blastemal cells.

Rare types of kidney cancer

Other rare types of kidney cancers are found in children. They are treated in a similar way to a Wilms' tumour but often more intensively. They include:

• clear cell sarcoma of the kidney (CCSK)

• malignant rhabdoid tumour of the kidney

• renal cell carcinoma - this is usually seen in teenagers

• mesoblastic nephroma - this is usually seen in very young babies and is usually a non cancerous tumour

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 their wee (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.