What Is a 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 5. Because doctors are getting better at spotting and treating this type of cancer, many children who have it will make a full recovery.

What Causes It?

All cancer is caused when cells in your body start to grow out of control. If your child has a Wilms tumor, their kidney cells didn’t mature like they were supposed to. Instead, they turned into cancer cells. Most of the time, this is due to a random change in a gene. It’s rarely inherited from a parent.

What Types Are There?

There are two kinds of Wilms tumors. The cells look different under a microscope.

Favorable histology: More than 9 out of 10 Wilms tumors fall into this group. It means that the cancer cells don’t vary widely. Children who have a “favorable histology” have a good chance of being cured.

Unfavorable histology: This type has a variety of deformed cancer cells. It can be much harder to cure.

Who’s at Risk?

Many things can put a child at risk of having a Wilms tumor.

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.

African-American. 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 that your child will get it are higher, too.

Certain birth defects. These can include testicles that haven’t dropped and hypospadias (the opening of the penis is on the underside instead of on the tip).

Another health problem. A Wilms tumor sometimes appears in children who have other rare conditions:

  • WAGR syndrome causes defects in the urinary tract.
  • Boys with Denys-Drash syndrome have testicles but also have female traits.
  • Microcephaly, which is when a baby is born with an abnormally small head.


What Are the Symptoms?

Children who have a Wilms tumor may have::

  • Pain, swelling, or growth im their belly. Many Wilms tumors get very big before they’re noticed, and this is sometimes the only sign of the disease. The average size is 1 pound.
  • Fever, nausea, or no interest in eating
  • High blood pressure
  • Blood in their pee

In some cases, kids won’t have any symptoms.

How Is It Diagnosed?

After a complete exam, your doctor will ask about your child’s symptoms and how long she’s had them. He’ll likely want to know if cancer or urinary tract problems run in your family.

Your doctor will also run some tests. This often includes a blood test,to check your child's kidney and liver function, and her red and white blood cells and blood clotting. A urine test is also performed to look for blood. An imaging test will also be done.

After blood work is done, the next test is usually an ultrasound of the abdomen. If a tumor in the kidney is found, it will need to be biopsied to make a diagnosis.

If a tumor is found, more tests will be needed. Your child's will order imaging of the chest. This will be done with an X-ray or CT scan. This test will be used to find out if the disease has spread beyond the kidney.

An ultrasound, MRI, or CT scan all can show a detailed view of your child’s kidneys.

What Is the 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, he may do a procedure called a radical nephrectomy. It removes the cancerous kidney, the ureter (the tube that carries pee away from the kidney), the adrenal gland on top of the kidney, and nearby tissue.

The doctor will also take out the lymph nodes near your child’s affected kidney. These are glands that help your body fight infection. Tests can be run on them to learn how much the cancer has spread.


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 she stays 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.

WebMD Medical Reference Reviewed by Sabrina Felson, MD on March 29, 2019


Mayo Clinic: “Wilms’ Tumor.”

American Cancer Society: “What is Cancer?” “What is Wilms’ Tumor?”

Kids Health from Nemours: “Wilms Tumor.”

Memorial Sloan Kettering Cancer Center: “About Wilm’s Tumor.”

CureSearch for Children’s Cancer: “Wilms Tumor in Children – In Treatment.”

St. Jude Children’s Research Hospital: “Wilms Tumor.”

The University of Texas M.D. Anderson Cancer Center: “Wilms’ Tumor Symptoms.”

Cancer.net/American Society of Clinical Oncology: “Childhood Cancer: Questions to Ask the Doctor.”

Cancer Research UK: “Wilms’ tumour (kidney cancer in children.)”

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