Wilms Tumor (Kidney Cancer)

What is Wilms tumor?

Wilms tumor is a type of kidney cancer that mainly affects children. The kidneys are two bean-shaped organs that filter blood and produce urine. They're located above the waist, one on either side of the spine.

Also called nephroblastoma, Wilms tumor is the fifth most common childhood cancer and one of the most common abdominal tumors in children. In the United States, about 400 children are diagnosed with the condition each year. Most often these children are under 3, though Wilms tumor can occur at any age between infancy and adolescence. It affects boys and girls equally.

The disease typically occurs in one kidney but occasionally involves both, and it sometimes spreads – usually to the lungs and liver. With treatment, most children with Wilms tumor can be cured.

Generally, the condition causes a painless swelling in the abdomen that parents discover while bathing or dressing the child or while changing diapers. Some children have abdominal pain, loss of appetite, bloody urine, fatigue or weight loss.

If a tumor may be present in your child's abdomen, don't apply pressure to the area. Your child should be handled carefully before and during any tumor evaluation. If the tumor ruptures, cancer cells can spread to other tissues of the body.

Causes of Wilms tumor

In most cases, the cause of this cancer is unknown. It typically develops in otherwise healthy children.

However, about 10% of cases occur in children with certain congenital conditions (those present at birth), such as aniridia (when the iris, or colored part of the eye, is partly or completely missing) and hemihypertrophy (when one side of the body is larger than the other). Wilms tumor also is associated with a number of rare genetic disorders, including:

• Beckwith-Wiedemann syndrome
• Denys-Drash syndrome
• Frasier syndrome
• Perlman syndrome
• Simpson-Golabi-Behmel syndrome
• WAGR syndrome

Patients may have a family history of the disease, though this is uncommon.

Signs & symptoms of Wilms tumor

Children with Wilms tumor may experience a variety of symptoms. The most common include:

• A painless mass or lump in the abdomen
• Pain in the abdomen
• Swelling of the abdomen
• Veins crossing the abdomen that appear distended or large
• Blood in the urine
• Decreased appetite
• Fever
• High blood pressure
• Weakness or fatigue

Diagnosis of Wilms tumor

Your child's doctor will gather a complete medical history and perform a physical exam. Tests to diagnose Wilms tumor may include:

• Blood and urine analyses. These provide information about kidney and liver function.
• Abdominal ultrasound. If Wilms tumor is suspected, the first imaging test ordered is often an ultrasound, which uses high-frequency sound waves to create pictures of internal organs and blood vessels. It can provide an outline of the kidneys and the tumor and show problems with the blood vessels exiting the kidneys or with other major veins in the abdomen.
• Abdominal computed tomography (CT) scan. A combination of X-rays and computer technology produces detailed cross-sectional images of the abdomen's inner structures, including the kidneys. This scan reveals specific information about the tumor and can show whether the cancer has spread to nearby lymph nodes, other organs or blood vessels.
• Magnetic resonance imaging (MRI) scan. This technique uses a combination of large magnets, radio frequency currents and a computer program to produce detailed images of organs and other structures in the body. MRI images can show whether the tumor has spread and whether it's compressing other organs in the area.
• Chest X-ray. This generates pictures of the heart, lungs and surrounding bones. The doctor may order a chest X-ray if they're concerned that the cancer may have spread to the lungs.

Imaging tests are usually sufficient to determine whether a child has Wilms tumor. But the diagnosis can be confirmed only by examining cells from the tumor under a microscope. Most often a tissue sample is obtained during surgery to remove the tumor. But if doctors aren't sure the cancer is Wilms tumor or can't completely remove the tumor, they may perform a biopsy, a procedure to take a very small piece of the tumor for microscopic analysis.

Staging of Wilms tumor

Part of the diagnostic process involves determining the cancer's stage – which helps doctors know how it's likely to behave and which treatment would be most effective. The stage is based on how much the cancer has spread and how the cells look under a microscope. The stages of Wilms tumor are:

• Stage 1. Cancer is found only in the kidney and can be completely removed by surgery.
• Stage 2. Cancer has spread only to areas near the kidney, such as fat, soft tissues, blood vessels or the renal sinus (a large area in the middle of the kidney housing blood vessels, lymphatic vessels and nervous tissue). The cancer can be completely removed by surgery.
• Stage 3. Cancer has spread to areas near the kidney, such as important blood vessels, other organs or nearby lymph nodes, and therefore can't be completely removed by surgery.
• Stage 4. Cancer has spread to organs farther from the kidney, such as the lungs, liver, bones and brain.
• Stage 5. Cancer cells are found in both kidneys.
• Recurrent. The cancer has reappeared after treatment. It may come back in the kidneys or another part of the body.

Treatment of Wilms tumor

The main techniques for treating Wilms tumor are surgery, chemotherapy and radiation therapy. Most children with Wilms tumor have more than one kind of treatment. The specific plan depends on the cancer's stage and the child's overall health.

Surgery

Treatment for Wilms tumor often begins with surgery to remove all or part of the affected kidney. (Bear in mind that people can live and be healthy with one kidney.) The surgery is also typically used to confirm the diagnosis.

The goal of surgery is to remove the entire tumor in one piece so that cancer cells don't spread to the abdomen. When this isn't possible, the surgeon may recommend other treatments first to shrink the tumor enough to be removed.

Depending on the nature of the tumor, the surgeon may perform one of the following operations:

• Partial nephrectomy. This involves removing the tumor and the part of the kidney surrounding it. This is typically done only in special cases, such as when the tumor is small or the child has only one working kidney.
• Simple nephrectomy. The entire affected kidney is removed. The other kidney can take on the full workload of filtering the blood.
• Radical nephrectomy. This procedure removes the entire kidney as well as surrounding tissues, including lymph nodes, and sometimes the adrenal gland (a small organ on the kidney that produces stress and other essential hormones).

Chemotherapy

Chemotherapy is using drugs to kill cancer cells. It's called a systemic treatment because the drug enters the bloodstream, travels throughout the body, and can kill cancer cells in many tissues and organs.

Chemo drugs for Wilms tumor are usually given either through an intravenous (IV) catheter (a thin, flexible tube) placed in a vein or through a central venous catheter, which is placed in a large blood vessel during surgery. The specific drugs, doses and length of treatment depend on the stage and other characteristic of the tumor and on the child's age.

Chemo may be given before surgery to shrink the tumor, making it easier to remove. Or it may be given after surgery to destroy any remaining cancer cells, an approach known as adjuvant chemotherapy.

In some cases, such as when the cancer has recurred, very high doses of chemo are used to kill the cancer cells. Because high-dose chemo also destroys bone marrow – the tissue inside bones where blood cells are formed – a child who receives this treatment will afterwards need a bone marrow (stem cell) transplant to replace the destroyed marrow cells. Therefore, before chemo begins, some healthy bone marrow tissue is taken from the bones and frozen for use later. Once chemo is completed, the stored bone marrow cells are returned to the patient intravenously. This is called an autologous bone marrow transplant because the patient's own cells are used.

Radiation therapy

Radiation therapy is using high-energy rays (usually X-rays) to kill cancer cells and shrink tumors. Radiation for Wilms tumor is usually delivered by a machine outside the body, so the treatment is called external beam radiation therapy (EBRT). Radiation may be used either before or after surgery and chemotherapy.

Both chemotherapy and EBRT affect healthy cells along with the cancer cells. Unfortunately, this damage causes some patients to develop a second type of cancer several years later. Clinical trials are underway to determine whether lower doses of chemotherapy and radiation could treat the cancer effectively while avoiding this long-term complication.

Though Wilms tumor can be cured, some patients don't respond to the standard treatments or can't tolerate their side effects. If either of these is the case for your child, they may have an opportunity to participate in a clinical trial (a study evaluating a promising new treatment) for Wilms tumor. Learn more about the process and potential benefits of enrolling your child in a clinical trial.