The short answer
Wilms tumor is the most common kidney cancer in children and usually affects young children. It is often found as a swelling or lump in the belly. Most children are treated with surgery and chemotherapy, and outcomes are generally good.
Wilms tumor is the most common type of kidney cancer in children.
It usually affects young children, most often under age 5.
It is often first noticed as a firm, smooth lump or swelling in the abdomen.
Treatment usually includes surgery to remove the affected kidney plus chemotherapy.
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The full explanation.
The simple version
Wilms tumor is the most common kidney cancer in children. Doctors also call it nephroblastoma. It starts in one kidney, usually in a child younger than 5. About 650 children in the United States get this diagnosis each year. Most children do very well with treatment.
How doctors find it
Many parents notice a firm, smooth lump in the child's belly. That is often the first sign. Other signs can include blood in the urine, a fever that will not go away, less appetite, weight loss, or belly pain. Sometimes doctors find the tumor during a routine checkup, before any symptoms show up.
Doctors confirm the diagnosis with imaging tests, like an ultrasound or a CT scan. Surgery to remove the tumor also lets doctors study the tissue closely. That tells them the exact type of Wilms tumor your child has.
Stage: how far the cancer has spread
Stage tells doctors how big the tumor is and whether it has spread. There are five stages, from I to V.
- Stage I: The tumor stays inside one kidney. Surgery removes it completely.
- Stage II: The tumor has grown into blood vessels or tissue near the kidney, but surgery still removes it all.
- Stage III: Some cancer remains in the belly after surgery, or it has reached nearby lymph nodes.
- Stage IV: The cancer has spread to organs farther away, like the lungs, liver, bones, or brain.
- Stage V: Both kidneys have a tumor at diagnosis.
What the cells look like
Doctors also check the tumor's histology — what the cancer cells look like under a microscope. Most Wilms tumors have "favorable" histology. The cells look close to normal, and the cancer usually responds well to treatment. A smaller number have "anaplastic" histology, meaning the cells look very abnormal. Anaplastic tumors need stronger treatment.
How it is treated
Treatment almost always starts with surgery. Doctors remove the affected kidney in an operation called a nephrectomy. They also remove nearby lymph nodes to check them for cancer cells. Most children live a full, healthy life with one working kidney.
After surgery, most children also get chemotherapy. Common drugs include vincristine, dactinomycin, and doxorubicin. The number of drugs and the length of treatment depend on the stage and the histology. Higher stages and anaplastic tumors need more chemotherapy, sometimes adding carboplatin, etoposide, cyclophosphamide, or ifosfamide.
Some children also need radiation therapy. This is more common at higher stages, or when the histology is anaplastic. Radiation can target the belly or, if the cancer has spread, the lungs or other affected areas.
When a tumor affects both kidneys (stage V), doctors usually start with chemotherapy to shrink the tumors first. They check the response with imaging around 6 to 12 weeks later. Surgery follows, and surgeons try to save as much healthy kidney tissue as possible.
Genetic conditions linked to Wilms tumor
A small number of children have a genetic condition that raises their risk, such as WAGR syndrome, Denys-Drash syndrome, or Beckwith-Wiedemann syndrome. Children with these conditions, or with related features like aniridia (a missing part of the iris) or hemihypertrophy (one side of the body larger than the other), usually get regular belly ultrasounds — often every 3 months until around age 8 — so a tumor can be caught early.
Late effects to watch for
Treatment can affect the heart, lungs, kidneys, and fertility later in life. Some survivors face a higher risk of a second cancer, including leukemia or cancer of the thyroid, breast, or skin. Ask your child's team for a written survivorship care plan. It should list what to watch for and when your child needs checkups.
When to call the doctor right away
Call your child's care team immediately for a fever of 100.4°F or higher during chemotherapy, unusual bleeding, new or worsening pain, or trouble breathing. Chemotherapy lowers blood counts for weeks at a time, and infections can turn serious fast while counts are low.
What to ask your team
Ask what stage and histology your child's tumor has. Ask whether radiation is part of the plan, and why. Ask what chemotherapy drugs your child will get and for how long. Ask for a written survivorship care plan for follow-up care once treatment ends.
Sources
Words to know
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Common questions
What is Wilms tumor?
Wilms tumor is the most common kidney cancer in children. It usually forms in one kidney but can sometimes affect both.
How is it usually found?
It is often first noticed as a firm, smooth lump or swelling in a child's belly, sometimes with abdominal pain, fever, or blood in the urine.
Who gets it?
It mainly affects young children, most often under age 5.
How is it treated?
Treatment usually includes surgery to remove the affected kidney, along with chemotherapy. Some children also receive radiation therapy depending on the stage and tumor features.
What is the outlook?
Outcomes for children with Wilms tumor are generally good. Your child's team can explain the outlook for their specific stage.
Questions to ask your doctor
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Last updated: 2026-08-20Next planned review: 2027-07-07
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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