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Paediatric Kidney Cancer · Warning Signs
Wilms tumour symptoms — abdominal lump in a child
Medically reviewed by the CION Paediatric Oncology Team · Last reviewed June 2026
A soft, painless lump on one side of your child's belly can be the first — and sometimes the only — sign of a Wilms tumour (nephroblastoma), the most common kidney tumour in young children. Knowing what to look for lets you act early, when treatment is most effective.
- Abdominal mass — firm, one-sided lump felt in the belly, often during bath time
- Blood in urine — pink or red-tinted urine, especially combined with belly swelling
- High blood pressure — kidney tumours can raise a child's blood pressure unexpectedly
- Tumour board care — every child at CION is reviewed by a dedicated paediatric oncology team
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Understanding Kidney Tumour in Children
What is a Wilms tumour (nephroblastoma)?
A short explanation every parent deserves before they search further.
Wilms tumour — also called nephroblastoma — is a type of cancer that starts in the kidney. It develops from immature kidney cells that did not mature normally before birth. The condition is named after Dr Max Wilms, who first described it in the 19th century.
It is the most common kidney tumour in children, and it most often appears between the ages of 3 and 5. Most children are diagnosed with a tumour affecting one kidney (unilateral), though in a smaller proportion of cases both kidneys may be affected (bilateral). The condition is very rarely seen in adults.
The encouraging reality is that, when caught at an early stage, Wilms tumour responds very well to treatment. A paediatric oncology team — working together across surgery, medicine, and radiation — can create a treatment plan that gives children the best chance of a full recovery while protecting as much healthy kidney tissue as possible.
This page is for parents who have noticed something — a lump, a change in urine colour, an unusual belly swelling — and want to understand what it could mean before their child's next appointment. It is not a substitute for a medical evaluation. If you have found a lump in your child's abdomen, please see a doctor today.
Did you know?
Wilms tumour (nephroblastoma) accounts for the large majority of all kidney cancers seen in children under 15 years of age. Globally, it is one of the paediatric cancers with the highest treatment response rates when identified early and managed by a specialist tumour board. Most children with localised disease go on to complete treatment and return to normal childhood activities. Early evaluation — starting with an ultrasound — is the single most important step a parent can take. (Source: National Wilms Tumour Study Group / Children's Oncology Group clinical evidence.)
Kidney tumour child signs
Wilms tumour symptoms — what to look for
Many symptoms are subtle. They can appear one at a time or together. Here is what each sign means and when to act.
Most common sign
Abdominal lump or swelling
A firm, smooth mass felt on one side of the belly — often the left or right flank — is the most frequently noticed sign of a Wilms tumour. Parents typically discover it during bath time or while dressing the child. The lump is usually painless on gentle touch. It does not cross the midline of the abdomen. Any unexplained abdominal mass in a child warrants same-day medical evaluation.
Urine changes
Blood in urine (haematuria)
Pink, red, or cola-coloured urine can signal blood — a sign that the tumour has irritated the kidney's collecting system. Haematuria occurs in roughly 1 in 5 children with Wilms tumour and is particularly significant when paired with an abdominal mass. Blood in urine always needs investigation, even if the child seems well otherwise. Many causes are benign, but it should never be assumed to be harmless without testing.
Less obvious
High blood pressure in a child
Kidney tumours can produce hormones or physically compress blood vessels in ways that raise blood pressure. Elevated blood pressure in a young child is always abnormal and should prompt investigation. It is often caught during a routine paediatric visit — another reason why regular well-child check-ups matter. On its own, high blood pressure rarely points specifically to Wilms tumour, but combined with an abdominal mass, it becomes a meaningful pattern.
General symptoms
Fever, fatigue, and poor appetite
Low-grade fever that has no clear infectious cause, persistent tiredness, and reduced interest in food are non-specific symptoms that can accompany many childhood illnesses — including Wilms tumour. On their own, these symptoms point to a wide range of causes. However, if your child has been unwell for more than two weeks and the paediatrician has not found an explanation, request an abdominal ultrasound as part of the work-up.
Abdominal discomfort
Belly pain or a sense of fullness
As a Wilms tumour grows larger, it can press on nearby organs and cause vague abdominal discomfort or a feeling that the belly is full even after small meals. Pain is not always present and — when it is — it is typically described as a dull ache rather than a sharp or cramping pain. A visibly distended (swollen) abdomen in a young child that is not explained by diet or constipation deserves prompt evaluation.
When to act urgently
Signs that need same-day evaluation
Take your child to a doctor the same day if you notice: a lump or firmness on one side of the belly, blood in the urine, a rapidly enlarging abdomen, or if a routine blood pressure check shows a high reading. These signs do not mean the diagnosis is certain — many causes are treatable and non-cancerous. What they mean is that prompt investigation — starting with an ultrasound — will give you an answer quickly and safely, without unnecessary anxiety.
These signs describe clinical presentations associated with Wilms tumour. A diagnosis can only be made by a qualified medical professional with appropriate investigations. This page does not constitute medical advice.
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What happens next
How doctors evaluate an abdominal mass in a child
Understanding the steps helps reduce anxiety. The process is methodical, not frightening.
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1
Clinical examination
The doctor will gently feel the abdomen to assess the size, side, consistency, and movement of any mass. Blood pressure will be measured. The doctor will also ask about the child's growth, any family history of kidney or cancer conditions, and associated symptoms such as blood in urine or unexplained fever. This step takes about 10–15 minutes and is not painful.
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2
Abdominal ultrasound
An ultrasound is the first imaging test. It uses sound waves — no radiation — and is painless for the child. It can confirm whether the mass is inside the kidney, estimate its size, assess blood flow within it, and check whether the opposite kidney is normal. An experienced sonologist can often give an initial impression the same day. This test is widely available and affordable.
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3
CT scan or MRI of the abdomen and chest
If the ultrasound suggests a kidney mass, a contrast-enhanced CT or MRI gives a detailed view of the tumour's relationship to surrounding blood vessels, the extent within or beyond the kidney, lymph node involvement, and whether the lungs show any metastatic nodules. In young children, MRI is preferred when possible to avoid radiation exposure. This imaging guides the surgical and treatment plan.
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4
Blood and urine tests
A full blood count, kidney function panel, and urine examination are standard. These tests assess how well the kidneys are working overall, check for anaemia (common in childhood cancers), and look for signs of infection or other causes of the symptoms. Results are typically available within 24 hours and are essential for planning treatment safely.
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At CION, every paediatric case is reviewed by a multidisciplinary tumour board — including a medical oncologist, surgical oncologist, and radiation oncologist — before any treatment decision is made. This is not one doctor's opinion; it is a team that considers the child's age, staging, imaging findings, and individual factors together. Your family receives a clear, written plan and time to ask questions before anything begins.
Did you know?
A small proportion of Wilms tumour cases are associated with certain genetic conditions — including WAGR syndrome, Denys-Drash syndrome, and Beckwith-Wiedemann syndrome. Children with these conditions may benefit from surveillance ultrasounds every three to four months during early childhood to detect tumours before any symptoms appear. If your child has been diagnosed with any of these syndromes, discuss a kidney surveillance plan with your paediatrician or a paediatric oncologist. (Source: Children's Oncology Group surveillance guidelines.)
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Common questions
Questions parents ask about Wilms tumour symptoms
What does a Wilms tumour feel like when you touch a child's belly?
A Wilms tumour typically feels like a smooth, firm lump on one side of the abdomen — most often the left or right flank. It is usually painless when touched gently, which is one reason parents may discover it accidentally during a bath or while dressing the child. The lump does not move across the midline. If you feel any unusual mass in your child's abdomen, see a doctor the same day. A proper ultrasound can clarify the nature of the lump quickly and safely.
At what age does Wilms tumour most commonly appear?
Wilms tumour most commonly occurs in children between the ages of 3 and 5 years, though it can appear in infants and older children up to about 10 years. It is rare in adults. The peak incidence is around 3 to 4 years of age. Early detection at any age gives children the best chance of successful treatment, so do not delay consulting a paediatric oncologist if a kidney tumour is suspected.
Is blood in my child's urine always a sign of Wilms tumour?
No — blood in a child's urine (haematuria) has many possible causes, including urinary tract infections, kidney stones, and other kidney conditions, most of which are not cancer. However, blood in the urine combined with an abdominal lump or swelling in a young child should always be investigated promptly. A doctor will arrange an ultrasound and urine tests to find the cause. Never assume or dismiss haematuria in a child — early evaluation is always the right step.
Can Wilms tumour be present without any symptoms?
Yes. In a significant number of cases, Wilms tumour is discovered accidentally — during a routine check-up or when a parent notices a one-sided abdominal swelling while bathing or hugging the child. The tumour can grow quite large before causing pain or other noticeable symptoms. This is why routine well-child check-ups are important, and why parents should not wait for symptoms like pain or fever to appear before seeking evaluation of any unusual abdominal lump.
What tests does a doctor use to diagnose Wilms tumour?
The first step is usually an abdominal ultrasound, which can identify a kidney mass quickly and without radiation. This is typically followed by a contrast CT scan or MRI of the abdomen and chest to understand the tumour's size, involvement of blood vessels, and whether it has spread to the lungs or lymph nodes. Blood tests and urine tests are done to check kidney function. A definitive diagnosis requires a biopsy or — in many cases — the tumour is removed surgically and then examined by a pathologist.
Should I take my child to a general paediatrician or a paediatric oncologist first?
Start with your child's paediatrician if that is what is accessible — they will arrange the initial ultrasound and, if a kidney mass is found, refer you to a paediatric oncologist immediately. If you have any access to a paediatric oncologist directly, you can go there first. At CION Cancer Clinics, a dedicated paediatric oncology team reviews every case in a tumour board — medical, surgical, and radiation oncologists together — so that your child's care plan is never a single doctor's opinion. Consultations are 45 minutes, giving your family time to understand every option.
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This page provides general health information for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Consult a qualified medical professional for any health concern.
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