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Wilms Tumor Facts

• What is Wilms tumor?
• What are the risk factors for Wilms tumor?
• What do we know about the biology of Wilms tumor?
• What are the symptoms of Wilms tumor?
• How is Wilms tumor diagnosed?
• How is Wilms tumor treated?
• What is the prognosis for survival for Wilms tumor?

What is Wilms tumor?

Wilms tumor is the most common type of kidney cancer in children, with about 500 cases diagnosed each year. Wilms tumors make up about 6% of all childhood cancers. Statistics show that out of 1 million children that are younger than 15 years old, 7.6 children are affected with Wilms tumor. Wilms tumor is most commonly diagnosed in children under the age of 5 years old, and rarely occurs in older children. Occasionally Wilms tumor has been diagnosed in adults. Wilms tumor affects only one kidney (unilateral) 95% of the time, while 5% of the time Wilms tumor affects both kidneys (bilateral).

What are the risk factors for Wilms tumor?

Wilms tumor normally develops in otherwise healthy children, however, 10% of cases occur in individuals with known congenital syndromes such as:

• WAGR Syndrome(Wilms tumor, Aniridia, Genitourinary malformation, and mental retardation)
• Denys-Drash Syndrome
• Beckwith-Wiedemann Syndrome

In addition, children with hemihypertrophy, cryptorchidism, and hypospadia have a higher risk for developing Wilms tumor. On rare occasions, Wilms tumor can run in families and can occur in siblings or cousins. Currently, there have been no documented or known environmental, chemical, or infectious agents that cause Wilms tumor.

The true risk estimate for children getting Wilms tumor is currently unknown and is studied as part of the clinical trials by the COG and SIOP. The risk might vary depending on the disease, e.g. it might be higher in patients with familial Wilms tumor, with Wilms tumor of both kidneys, or with Wilms tumor that is associated with a syndrome. Of 191 children born to 99 patients with unilateral Wilms tumor, none developed Wilms tumor.

What do we know about the biology of Wilms tumor?

The development of Wilms tumor is thought to involve changes in a number of genes that work to control normal kidney development and growth. The syndromes associated with Wilms tumor have provided clues to the genetic basis of the disease.

The first gene, WT1, is associated with WAGR syndrome and Denys-Drash syndrome and is located on chromosome 11p13. A second gene, WT2, is associated with the Beckwith -Wiedemann syndrome and is located on chromosome 11p15. Several other genes have been discovered to be involved with Familial Wilms tumor, such as FWT1, which is located on chromosome 17q, and FWT2, which is located on chromosome 19q.

More information about the biology of Wilms tumor and current research in Wilms tumor.

What are the symptoms of Wilms tumor?

The most common signs and symptoms in patients with Wilms tumor might include:

• A hard lump or mass in the abdomen
• Abdominal pain or swelling
• Blood in the urine
• Fever (without a reason)
• High blood pressure

It is important to realize that each child will experience the symptoms differently. The symptoms of Wilms tumor might resemble other medical conditions and illnesses. A physician should be seen for the correct diagnosis for the symptoms.

How is Wilms tumor diagnosed?

In order to diagnose Wilms tumor, an initial medical history and physical examination is performed by the child's physician. During the examination your doctor should check your child for symptoms of:

• Aniridia (absence of the colored part of the eye (iris) at birth)
• Hemihypertrophy (one side of the body is larger than the other side)
• Genitourinary abnormalities such as hypospadia, cryptorchidism or pseudohermaphroditism

The first test used to diagnose Wilms tumor is often an abdominal ultrasound. A specialized ultrasound called a Doppler ultrasound is done to evaluate if the tumor has grown into the blood vessels. This is usually followed by a CT scan and/or MRI scan of the abdomen and pelvis to further evaluate the mass.

In addition, several imaging studies are used to make sure the tumor has not spread to other organs. A CT scan of the lung allows a doctor to see if the mass in the kidney has spread to the lung. Chest x-rays (CXR) are often done in addition to CT scans, and are used mostly during and after treatment. A PET scan may be done if it is available and if your child can hold still long enough for it.

Once the diagnosis of Wilms tumor has been confirmed by a pathologist, the oncologist will evaluate the results and assign a stage to the tumor. Staging means, assessing the characteristics of the tumor, whether it has spread, and if the surgeon was able to remove the entire tumor. The stage of the tumor and other characteristics will help determine what type of treatment your child will have.

How is Wilms tumor treated?

Wilms tumor treatment has progressed greatly over the past thirty years. Children with Wilms tunor are currently treated with a combination of chemotherapy, surgery, and in some cases radiation. The current recommendations are to remove the tumor first, then continue with chemotherapy and if needed, radiation. Tumors that can not be completely removed or that have spread to multiple places should be biopsied first. Following a biopsy of the tumor, chemotherapy is given to shrink the tumor. Re-evaluation for surgery is done at a later time.

The majority of children in the United States are treated on a Phase III clinical trial. Clinical trials offer the most up-to-date treatments combined with state of the art research.

The exact treatment your child will receive depends on 3 factors:

1) The appearance of the tumor under the microscope

The appearance of Wilms tumor is used to separate Wilms tumor into two mains groups:

• Wilms Tumor with favorable histology
• Wilms Tumor with unfavorable histology (Anaplastic Wilms tumor)
  • Focal Anaplastic
  • Diffuse Anaplastic

2) The stage of the tumor

The stage tells the doctor if the cancer has spread and if the surgeon was able to remove the tumor.

• Stage I: Tumor was only in 1 kidney and was completely removed.
• Stage II: Tumor was outside the kidney, but completely removed.
• Stage III: The tumor has spread locally or within the abdomen and could not be completely removed.
• Stage IV: The tumor spread through the blood to other areas such as the lung, liver, or lymph nodes.
• Stage V: Tumor was in both kidneys at diagnosis.

Of the children diagnosed with Wilms tumor, 40% have stage I disease, 25% have stage II disease, 25% have stage III disease, 10% have stage IV disease, and 5% have stage V disease.

3) Test results from the molecular biology studies (if your child participated in a clinical trial)

Loss of heterozygosity (LOH) of chromosomes 16q and 1p

Abnormalities on chromosome 16q have been found in approximately 20% of Wilms tumors, and on chromosome 1p in 10% of Wilms tumors. These abnormalities are associated with a lower cure rate and are used in the current clinical trial by the Children's Oncology group to decide on the specific therapy for patients with Wilms tumor. The exact role and function of the genes on chromosome 16q and 1p, and their biological significance in Wilms tumor is currently unknown.

Children who have LOH at these two places have different treatments than children with no LOH. Children with LOH will be treated with the current phase III clinical trial through the Children's Oncology Group, which is a more intense chemotherapy than that normally used at diagnosis of Wilms tumor. It is hoped that the increase in intensity will improve cure rates in this group.

What is the prognosis for survival for Wilms tumor?

Favorable Wilms Tumor

• Stage I: 10 year relapse free survival rate of 91% and a 10 year overall survival rate of 96%
• Stage II: 10 year relapse free survival rate of 85% and a 10 year overall survival rate of 93%
• Stage III: 10 year relapse free survival rate of 84% and a 4 year overall survival rate of 89%
• Stage IV: 10 year relapse free survival rate of 75% and a 10 year overall survival rate of 81%

Unfavorable Wilms Tumor

• Stage I: 2 year relapse free survival rate of 65%
• Stage II: 2 year relapse free survival rate of 79%
• Stage III: 2 year relapse free survival rate of 62%
• Stage IV: 2 year relapse free survival rate of 33%

It is important to realize that the prognosis percentage is statistical, meaning it refers to groups of children with Wilms tumor, not individual children with Wilms tumor. For example, a child with stage I favorable Wilms tumor is not 91% cured. The child is either cured or has a relapse (the tumor reappears), but he or she has a 91% chance of being cured out of all of the children within that group. So, in a group of 100 children, 91 children will never have the cancer come back (relapse free survival rate). The overall survival rate refers to how many children will still be alive after 10years. So, in a group of 100 children with stage I favorable Wilms tumor, 96 children will still be alive after 10 years. The four children who did not survive after 10 years may not have died from the tumor itself, but death may have resulted from a different cause (e.g. complications in treatment, car accident, etc.).

Written and reviewed by: Susanne Ragg, MD, PhD; Deannie Lee, MD, PhD; Mary M Davis MD; James Hill, MD; Mercy Odueyungbo, B.S.; Ann Haddix, RN, MSN, CPNP; Jada Paine, MS; Julie Haydon, BS; Michelle Lucke, MPH; Elaine Skopelja, MALS, AHIP; Kellie Kaneshiro, AMLS, AHIP. Amber McMahon, B.S. Date last reviewed: August 2006.