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What is Wilms' Tumor?

A Wilms’ tumor [VILMZ TOO-mer] can also be called a nephroblastoma [NEF-roh-bla-STOH-muh] or Wilms’ cancer. While it is the most common type of kidney cancer in children, it is rare, with only about 650 cases in the U.S. each year. It usually starts with only one kidney with a single tumor. In a few cases, it is found in both kidneys, or more than one tumor is found in a single kidney.

Doctors think that the tumor might begin forming before birth. Most cases involve children under the age of 5 years. It has been seen in infants, older children, and some adults.

Some children are at higher risk for getting a Wilms’ tumor because they have related syndromes. If your child is known to have a risk factor, they will be screened for this cancer every 3 months with an ultrasound until they are older than 5 years.

A Wilms’ tumor is often painless. By the time that it can be felt as a lump in the abdomen, most Wilms’ tumors are very large. They can grow to be larger than the kidney itself. Most are found before the cancer can spread to other parts of the body. Usually, if the cancer spreads, it goes to the lungs first.

A Wilms’ tumor can be very fragile. A biopsy is not part of the testing to diagnose it. Instead, imaging studies are done before oncologic surgery, a type of surgery to remove cancers.

Most of the time, your child will have a surgery to remove all or part of the kidney with the tumor. After the surgery, a pathologist [puh-THOL-uh-jist] will look at a piece of the tumor under a microscope. Then, they can confirm whether or not it’s a Wilms’ tumor.

By looking at the tumor, a pathologist can group it into one of 2 main types of Wilms’ tumors:

  1. Favorable. More than 90 out of 100 times, a Wilms’ tumor is made of cancer cells that look about the same.
  2. Unfavorable. These cases show many cancer cells that look different. The more differences found the more aggressive treatment needs to be. This kind of tumor is called an anaplastic [an-uh-PLAS-tik] Wilms’ tumor.

Surgery is often followed by chemotherapy [kee-moh-THER-uh-pee]. In rare cases where the tumor is too big to remove, chemotherapy is used to shrink it before surgery. Your child might also need radiation therapy.

A Wilms’ tumor prognosis is very good in almost all cases. The outlook is still good even if the cancer returns —which it sometimes does and usually within 2 years —because Wilms’ tumor treatment continues to improve. Some cases cannot be cured or are cured with long-term side effects, such as needing dialysis.


Even with a Wilms’ tumor, your child may act like normal. The tumor might not cause pain. The most obvious of Wilms’ tumor symptoms is a firm lump that can be felt in the area of your child’s belly.

Sometimes, a child may show these signs:

  • Feeling queasy (nausea)
  • Not being hungry
  • Vomiting
  • Pain in the stomach
  • Constipation
  • High blood pressure
  • Being short of breath
  • Blood in their pee
  • Fever

When to See a Doctor

You should take your child to see a doctor if you can:

  • Feel a lump in their belly
  • Feel swelling in their belly
  • Tell that your child has pain in their belly

You should also check with a doctor if your child shows other Wilms’ tumor symptoms. Even though the cancer is rare and may not be the cause, it’s important to check out symptoms that are worrying you.

If your child has one of the syndromes that may cause a Wilms’ tumor or another risk factor, they will be screened every 3 months until they are older than 5 years. If they are at high risk, these screenings may be done even longer.


Doctors don’t know exactly what causes a Wilms’ tumor. They think that it begins before birth when your child’s DNA makes a mistake while forming the kidneys.

Three rare syndromes have been known to cause Wilms’ tumors:

  1. WAGR syndrome. This syndrome causes the iris of the eye not to form, genital abnormalities, and learning disabilities.
  2. Denys-Drash syndrome. This syndrome causes kidney disease, and reproductive organs or external sexual characteristics of both a male and a female.
  3. Beckwith-Wiedemann syndrome. This syndrome causes larger than average body size as well as an enlarged tongue and internal organs, ear abnormalities, and other cancers.

Certain things can increase your child’s chances of getting a Wilms’ tumor, including:

  • Aniridia [ann-ahy-RID-ee-uh]. Aniridia is the absence of an iris of the eye. Even if it’s not part of WAGR syndrome, having it is a risk factor for a Wilms’ tumor.
  • Hemihypertrophy [HEH-mee-HY-pur-TRO-fee]. This condition causes one side or one body part to be larger than the other side.
  • Family health history. It is rare for a gene mutation to cause a Wilms’ tumor to be passed from either parent to your child. However, if your child does have a family history of this kind of tumor, they do have a higher risk of getting it. It’s possible to have your child’s DNA tested for any of the known gene mutations for Wilms’ tumor or related syndromes. This is called genetic testing.

Diagnosis and Tests

If a lump or mass is found in your child’s stomach area, your child’s doctor will order diagnostic tests, such as:

  • Urinalysis, which checks your child’s pee for signs of problems
  • Blood test, which checks your child’s blood for signs like low or high cell counts
  • Imaging studies

While the urine and blood tests can’t find a Wilms’ tumor, they provide information that doctors can use. The imaging studies are more useful in finding out the size and shape of a tumor, and some images might be taken of other areas to show if the cancer has spread. The kinds of imaging studies done include:

  • X-ray
  • Ultrasound
  • CT scan
  • MRI
  • Bone scan
  • PET scan or PET-CT scan

Your child’s doctor may also want to do a procedure called a cystoscopy [si-STOS-kuh-pee]. This uses a cystoscope, a tube with a camera at the end that is inserted between your child’s legs. With it, a doctor can look at your child’s bladder.

Because more than 95 out of 100 kidney tumors are Wilms’ tumors, finding a mass in the kidney usually leads to this diagnosis. Unlike with other cancers, a biopsy will not be done to confirm a diagnosis of a Wilms’ tumor. A Wilms’ tumor is more fragile than other tumors. A biopsy of the tumor would put your child at risk of cancer cells being spread through the abdomen.

Instead, the diagnosis of Wilms’ tumor is confirmed after the surgery when the pathology report is made. During the surgery, lymph [limf] nodes may also be removed and then checked for cancer cells by the pathologist.


Using the results of all these tests, your child’s doctor will stage your child’s cancer. A stage reflects how big the cancer has grown and how much it has spread.

The stages for a Wilms’ tumor go from Stage I [1] to Stage V [5]:

  1. Stage I. The cancer is in a single kidney where it is fully contained. It can be completely removed with surgery.
  2. Stage II. The cancer has moved outside the kidney to nearby tissues or blood vessels. It can be completely removed with surgery.
  3. Stage III. The cancer has spread to the lymph nodes or to other nearby organs, but it has not spread outside the abdomen. It might break open. It has to be removed in pieces, or it cannot be completely removed with surgery.
  4. Stage IV. The cancer has spread to distant lymph nodes or organs, such as the lungs, liver, brain, or bones.
  5. Stage V. The cancer was found in both kidneys.
When Wilms’ tumors are found in both kidneys (Stage V), each kidney’s tumor is given its own stage.


Wilms’ tumor treatment usually combines surgery and chemotherapy. Sometimes, radiation therapy is also used. Treatment is guided by the stage of the cancer.

  • Surgery. Most of the time, treatment begins with surgery. The surgeon will try to remove the whole tumor and some of the healthy tissue around it. The healthy tissue that is taken is called the margin. If only one kidney is known to be affected, the surgeon can look at the other kidney for signs of cancer. The surgery may involve removing:
    • Part of one kidney
    • All of one kidney
    • Part of each kidney
    • Both kidneys (rare)
  • Chemotherapy. Chemotherapy medicines are very strong and are put into your child’s whole body. Chemotherapy after surgery is used to kill any cancer cells that might have been missed during surgery or just could not be removed. For very large tumors, chemotherapy might be used before surgery to shrink them. This will make it easier to remove the entire tumor. Chemotherapy is also given before surgery in Stage V cases when the tumors are found in both kidneys. This makes it more likely that both kidneys do not need to be fully removed.
  • Radiation therapy. More advanced stages of Wilms’ tumor may be treated with radiation. This kind of therapy uses high-energy x-ray beams to kill cancer cells. Your child will be placed on a table while the machine that delivers the radiation moves around them.

Your child can lead a full, healthy life with one kidney or with partial kidneys. Having both kidneys removed would mean that your child would need dialysis or a kidney transplant from a donor.

Chemotherapy and radiation come with both short-term and long-term side effects:

  • Short-term side effects of chemotherapy include nausea, vomiting, not being hungry, hair loss, and an increased risk of infections.
  • Short-term side effects of radiation may include nausea, diarrhea, being tired, and having irritated, red skin like a sunburn would cause.
  • Long-term side effects include developing another type of cancer such as leukemia and weakening other organs. The risk of having these side effects happen is very low compared to the benefit of treatment.


A Wilms’ tumor can’t be prevented.

After birth, if your child shows risk factors for getting a Wilms’ tumor, they will undergo regular screening with ultrasounds of their kidneys. This screening may find the cancer in an earlier, more treatable stage. Early treatment may prevent more problems. 

A Wilms’ tumor [VILMZ TOO-mer] is the most common kind of kidney cancer in children. However, it is rare with only about 650 new cases in the U.S. each year. Most cases involve children under the age of 5.