Patient Basics: Wilms Tumor

Wilms tumor, also called nephroblastoma, is a kidney cancer that mainly affects young children, most often between ages 3 and 4. The most common first sign is a painless lump or swelling in the belly. Wilms tumor is rare, and treatment works very well. About 9 in 10 children with Wilms tumor are cured.

Key points

• It’s the most common kidney cancer in children, with about 500 new cases a year in the US.
• It usually affects one kidney, but sometimes both.
• Most cases are not inherited and are not caused by anything a parent did or didn’t do.
• Treatment usually combines surgery to remove the tumor with chemotherapy, and sometimes radiation.
• Children with certain genetic syndromes have a higher risk and get regular kidney ultrasounds.

What causes Wilms tumor

Before birth, the kidneys develop from immature cells that normally mature by the time a baby is born. In Wilms tumor, a few of these early cells keep growing instead of maturing, and form a tumor. Changes in genes that control kidney growth, such as WT1, are often involved. These gene changes usually happen by chance in the kidney cells and aren’t passed down in the family.

A small number of children have a birth difference or syndrome that raises the risk, including:

• Missing or partly missing irises, the colored part of the eye (aniridia)
• One side of the body growing larger than the other (hemihypertrophy)
• Beckwith-Wiedemann syndrome, a condition with overgrowth and a large tongue
• WAGR syndrome and Denys-Drash syndrome
• Undescended testicles or a urinary opening on the underside of the penis (hypospadias), together with other features

These children usually have a kidney ultrasound every 3 months until about age 7 or 8, so a tumor can be found early. A few families have an inherited form, which is why the care team asks about relatives with childhood kidney tumors.

Wilms tumor symptoms

• A firm, smooth lump or swelling in the belly, often noticed by a parent during a bath or while dressing the child
• Belly pain
• Blood in the urine, or urine that looks pink or brown
• Fever without a clear cause
• Poor appetite, nausea, vomiting or constipation
• High blood pressure, found at a checkup

Many children feel and act well, which is why a belly lump can be the only clue. If you feel one, don’t keep pressing on it, and have your child seen soon.

How Wilms tumor is diagnosed

• Exam. The doctor gently feels the belly, checks blood pressure and looks for features of related syndromes.
• Ultrasound of the belly is usually the first imaging test. It shows a mass in the kidney and checks the large vein that drains it.
• CT or MRI of the belly gives a clearer picture of the tumor, the other kidney and nearby organs. A chest CT checks the lungs, the most common place for Wilms tumor to spread.
• Blood and urine tests check kidney and liver function and blood counts.

In the US, the tumor is usually removed in surgery before any biopsy, because poking it with a needle can spread cancer cells. A pathologist then examines the whole tumor. Most Wilms tumors have “favorable histology,” meaning the cells look less aggressive. A smaller group, called anaplastic, needs stronger treatment.

The stage runs from I to V. Stage I means the tumor was only in the kidney and was removed completely. Stages II to IV mean it has spread further. Stage V means both kidneys have tumors.

How Wilms tumor is treated

Children do best when treated at a children’s cancer center, by a team that includes a pediatric surgeon, a pediatric oncologist and a radiation oncologist. Many children take part in clinical trials, which have helped raise cure rates.

• Surgery. The surgeon usually removes the whole affected kidney (nephrectomy) and checks nearby lymph nodes. When both kidneys are affected, the team gives chemotherapy first to shrink the tumors, then removes only the tumors to save as much kidney as possible.
• Chemotherapy. Common drugs include vincristine and dactinomycin, with doxorubicin or others added for higher stages. A few very small, low-risk tumors in babies need surgery alone.
• Radiation therapy is added for some higher-stage or anaplastic tumors, or when cancer has spread to the lungs.

Side effects of treatment can include hair loss, nausea, tiredness and a higher risk of infection. Most of these go away after treatment ends. The team will give you a plan for fevers and for when to call.

After treatment

Children have regular checkups and scans for several years, since most relapses happen within the first two years. Almost all children who have one kidney removed live normal lives. The remaining kidney grows a little and takes over the work. Your child’s blood pressure and kidney function will be checked over time.

Some treatments can cause late effects years later, such as heart problems from doxorubicin, slower growth in areas that got radiation, fertility problems or, rarely, a second cancer. A survivorship clinic watches for these into adulthood. Child life specialists, social workers and support groups can help your child, siblings and the whole family through treatment.

When to see a doctor

• A lump or swelling in your child’s belly
• Blood in your child’s urine
• Ongoing belly pain, fever or poor appetite without a clear cause

During treatment, call the care team right away for a fever of 100.4°F (38°C) or higher, signs of infection, bleeding or bruising, or vomiting that keeps your child from drinking. Get emergency care for sudden, severe belly pain.

Common questions about Wilms tumor

Is Wilms tumor curable?

Yes, in most children. Around 9 in 10 children with Wilms tumor are cured, and the rate is even higher for early-stage tumors with favorable cells. Children whose tumors have spread or have anaplastic cells need more treatment, and many of them are cured too.

Is Wilms tumor hereditary?

Usually not. Only about 1 or 2 in 100 children with Wilms tumor have a relative who had it. More often, the risk comes from a genetic syndrome that happened by chance. A genetic counselor can explain whether your child’s siblings or future children need screening.

Can a child live normally with one kidney?

Yes. One healthy kidney can do the work of two, and most children grow up to be active, healthy adults. Your child’s doctor will check blood pressure and urine over the years. Ask whether to protect the remaining kidney during contact sports.

Can adults get Wilms tumor?

Rarely. Almost all cases are in children under 10, and most are under 5. Adults who get Wilms tumor are treated with similar surgery and chemotherapy, ideally at a center that has experience with this tumor, since most adult kidney cancers are a different type.

Questions to ask your doctor

• What stage is my child’s tumor, and are the cells favorable or anaplastic?
• What treatment do you recommend, and how long will it last?
• Is there a clinical trial for my child?
• What side effects and late effects should we watch for?
• Should my child or our family see a genetic counselor?

Learn more

• Wilms tumor and other childhood kidney tumors (National Cancer Institute)
• Wilms tumor (MedlinePlus, U.S. National Library of Medicine)

This guide is general information and doesn’t replace advice from your own doctor. Last updated October 2026.