An Overview of Wilms Tumor

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Wilms tumor (also called nephroblastoma) is a childhood cancer that affects the kidneys. A large mass within a child's abdomen or abdominal swelling is usually the first sign. This mass or swelling is often noticed incidentally when a parent is changing or bathing their child.

Diagnosing Wilm's tumor is a multi-step process and involves a medical history, physical examination, and various blood and imaging tests. A biopsy (tissue sample) is needed to confirm the diagnosis. Surgery is the primary treatment for Wilms tumor, often followed by chemotherapy, and in some cases, radiation therapy.

Child with cancer and her doctor
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There are around 650 new cases of Wilms tumor in the United States every year. This childhood cancer most commonly occurs between the ages of 3 to 5 years and is slightly more common in girls.


Most of the time, a child with Wilms tumor will only have a swollen belly or abdomen. Sometimes, a hard bump or mass can be felt. The abdominal swelling or mass are from the tumor growing to be way larger than the kidney from which it started.

Other symptoms and signs of a Wilms tumor may include:

  • Abdominal pain
  • Blood in the urine (called hematuria)
  • Fever
  • High blood pressure

The good news is that most cases of Wilms tumor are caught before the cancer has had a chance to spread to other parts of the body (called metastasis).

However, if the cancer does spread, it often goes to the lungs first. In these cases, a child may have report trouble breathing.


Wilms tumor arises from immature kidney cells that grow uncontrollably. You have two kidneys, which are bean-shaped organs located in each flank (the area at the back of your abdomen, beneath your ribcage, and adjacent to your spine).

In the womb, a fetus's kidneys develop early. But sometimes, cells that are supposed to become kidney cells do not mature—they remain immature within the baby's kidney or kidneys. These immature cells may then mature around the time a child is 3 to 4 years old, or they may grow uncontrollably and form a Wilms tumor.

Most Wilms tumors affect only one kidney. Approximately 5% to 10% of children with Wilms tumor have both kidneys affected.

Researchers are not exactly sure why, in some children, early kidney cells eventually form a Wilms tumor.

They suspect that various and multiple gene mutations (when the DNA sequence of a gene changes) are involved. These gene mutations may be inherited (passed from mom or dad) or be random and spontaneous (occur on their own).

The role of gene changes in the development of Wilms tumor is supported by the fact that children with certain genetic syndromes are at an increased risk for developing this cancer.

While not an exhaustive list, some genetic syndromes associated with Wilms tumor include:

Most cases of Wilms tumor are not due to inherited gene mutations. In other words, experts believe most cases of Wilms tumors occur randomly.


The diagnosis of Wilms tumor begins with a medical history and physical examination. If the diagnosis is suspected, a child will be referred to a pediatric cancer center .

To confirm the diagnosis, tissue from the tumor will be examined under the microscope by a doctor called a pathologist.

Tissue can be obtained through a biopsy or during surgery when the tumor is being removed.

During the diagnostic process, a urinalysis and lab tests, such as a comprehensive metabolic panel and a complete blood count, will be ordered. These tests are useful in evaluating the kidney and other organs' functioning (in case the tumor has spread).

Imaging tests are also performed to help distinguish Wilms tumor from other masses in the abdomen, and for the eventual staging of the cancer.

These imaging tests often include:


The treatment for Wilms tumor involves, surgery, chemotherapy, and in some children, radiation.


Most children with Wilms tumor will undergo surgical removal of the entire kidney (called a radical nephrectomy).

Along with the removal of the kidney, the adrenal gland (which sits on top of the kidney), the ureter (which carries urine from the kidney to the bladder), and the fatty tissue that surrounds the kidney will be removed.

During the surgery, lymph nodes adjacent to the kidney will also be removed and tested to see if cancer cells are present. Lymph node sampling is important for staging a child's cancer and determining their treatment plan after surgery.


Chemotherapy is usually given after surgery in children with Wilms tumor. Exceptions may include very young children with early-stage, small (less than 550 grams) Wilms tumors that have a favorable histology (what the cells look like under the microscope).

In children with Wilm tumors on both kidneys, chemotherapy is usually given before surgery to try and shrink the tumors.


Radiation therapy is used to treat more advanced stages of Wilms tumor.

Radiation is also used to treat earlier-stage tumors that have anaplastic histology, which means the appearance of the cancer cells is distorted—this makes the tumor harder to treat.


There are no known factors associated with the development of Wilms tumor, meaning there is no chemical or lifestyle habit, for example, that is known to cause a Wilms tumor. Therefore, there is no way to prevent this type of cancer.

However, if a child has a syndrome associated with an increased risk for developing Wilms tumor (for example, WAGR or Beckwith-Wiedemann syndrome), regular screening with an abdominal or kidney ultrasound is recommended.

A Word From Verywell

If your child was diagnosed with Wilms tumor, please reach out to your child's cancer team for help with coping with the diagnosis.

The physical and emotional effects of caring for your child as he or she undergoes treatment can be overwhelming. Please know that you are not alone—with knowledge, support from others, and resiliency, you and your family and child can get through this.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Colleen Doherty, MD
 Colleen Doherty, MD, is a board-certified internist living with multiple sclerosis.