Wilms Tumor

What Is Wilms Tumor?

A Wilms tumor (also called a nephroblastoma) is the most common kidney cancer in children. Most children with it have a tumor on one kidney, but about 5% get a tumor on both.

The reasons aren’t clear, but it most often affects kids who are 3 to 4 years old. It’s much less common after age 5. Doctors are getting better at spotting and treating this type of cancer, so many children who have it will make a full recovery.

Wilms Tumor Symptoms

Some children who have a Wilms tumor won’t notice symptoms. Others may have:

  • Belly pain
  • Swelling in their belly
  • A growth that you can see or feel in their belly
  • Fever
  • Nausea
  • Lack of appetite
  • High blood pressure
  • Blood in their pee
  • Constipation
  • Shortness of breath

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Many Wilms tumors get very big before anyone notices them. They’re sometimes the only sign of the disease. The average size is 1 pound.

Wilms Tumor Causes

All cancers happen when cells in your body start to grow out of control. If your child has a Wilms tumor, their kidney cells didn’t grow like they should have. Instead, they turned into cancer cells. Most of the time, this is because of a random change in a gene. Rarely, it’s because of gene changes handed down from a parent.

Wilms Tumor Risk Factors

Things that might make a child more likely to have a Wilms tumor include:

  • Age. Most children who get this type of cancer are between 3 and 5 years old.
  • Gender. Girls are more likely to have it than boys.
  • Race. Black children are slightly more likely to get a Wilms tumor than children of other races.
  • Family history. If someone in your family has had a Wilms tumor, the odds are higher that your child will get it, too.
  • Birth defects. These can include:
  • Testicles that haven’t dropped (cryptorchidism)
  • The opening of the penis is on the underside instead of on the tip (hypospadias)
  • A total or partial lack of the colored area of the eye (aniridia)
  • An oversized arm or leg (hemihyphertrophy)
  • WAGR syndrome causes problems in the urinary tract.
  • Boys with Denys-Drash syndrome have testicles but also have female traits.
  • Microcephaly is when a baby is born with an unusually small head.
  • Beckwith-Wiedemann syndrome causes internal organs that are larger than usual.

Types of Wilms Tumors

There are two kinds of Wilms tumors, divided by how the cells look under a microscope.

  • Favorable histology. More than 9 out of 10 Wilms tumors fall into this group. It means there isn’t a lot of difference among the cancer cells. Children with this type have a good chance of being cured.
  • Unfavorable or anaplastic histology. This type has a variety of deformed cancer cells. It can be much harder to cure.

Wilms Tumor Diagnosis

Your child’s medical appointment will probably include:

  • A physical exam and medical history. Your doctor will ask about the symptoms and whether cancer or urinary tract problems run in your family.
  • A blood test to check how well your child's kidneys and liver are working, their red and white blood cells, and their blood clotting.
  • A urine test to look for blood
  • Imaging tests like an ultrasound, MRI, or CT scan of your child’s belly

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If the doctor finds a tumor in your child’s kidney, they may:

  • Take a small sample to look at under a microscope (biopsy)
  • Order more imaging tests to find out whether the disease has spread
  • Do a bone scan to look for diseased bone

Wilms Tumor Staging

Your doctor will use test results to figure out how far a tumor has spread. This is called staging. The stages of a Wilms tumor are:

  • Stage I. It’s in only one kidney. Surgery can remove it all.
  • Stage II. Cancer has moved into the area around the kidney, but surgery can remove it all.
  • Stage III. Cancer hasn’t spread outside the child’s abdomen. Surgery can’t remove it all.
  • Stage IV. Cancer has spread to parts of the body that are farther away, like the lungs, bones, or brain, or to lymph nodes outside the belly.
  • Stage V. There are tumors in both kidneys.

Wilms Tumor Treatment

How a Wilms tumor is treated depends on how much the cancer has spread. It can include surgery, chemotherapy, and radiation therapy.


If your doctor operates, they may do one of these procedures:

  • Partial nephrectomy. This removes the tumor and some healthy tissue around it.
  • Radical nephrectomy. This removes the affected kidney, the ureter (the tube that carries pee away from the kidney), the adrenal gland on top of the kidney, and nearby tissue.
  • Removal of both kidneys. In some cases, the doctor will need to take out both kidneys. Your child would then need to have dialysis, using a machine to filter waste out of their blood. Once they’re healthy enough, they might have a kidney transplant.

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Certain medications can fight or kill cancer cells inside your child’s body. Most children who have Wilms tumors will get chemo at some point during treatment. These drugs can also affect healthy cells, leading to side effects including:

  • Hair loss
  • Fatigue
  • Mouth sores
  • Loss of appetite
  • Nausea and vomiting
  • Diarrhea or constipation
  • Bruising or bleeding easier than usual
  • Higher chances of infection

Your medical team will often be able to manage side effects.


Strong radiation can also kill cancer cells. A machine focuses it onto the cancer.

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Doctors tend to use radiation for tumors that are stage III and above. But it can also have short-term and long-term side effects, including tissue damage, so they’ll use as little as possible.

Wilms Tumor Outlook

The outlook for most kids with a Wilms tumor is good. Up to 90% of children who have a tumor with favorable histology can be cured. If the tumor has unfavorable histology, the cure rate is lower.

Once cancer treatment ends, your child will have regular doctor visits to make sure they stay healthy.

If there’s something you don’t understand, make sure to ask your doctor. This will help you know how to best to support your child.

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