Wilms' tumor is a rare kidney cancer that primarily affects children. Also known as nephroblastoma, it's the most common malignant tumor of the kidneys in children. The peak time of Wilms' tumor occurrence is at age 3, and it occurs only rarely after age 8.

Wilms' tumor may arise in either or both kidneys. The condition is named for the 19th-century German surgeon who recognized that the cancer develops from immature kidney cells.

The outlook for children with Wilms' tumor has greatly improved in recent decades. Improved imaging techniques help doctors to determine the extent of the cancer in Wilms' tumor and to plan treatment.

You may feel a mass in your child's abdomen during bathing or dressing, or your child's doctor may detect it during a routine physical examination. The tumor may be firm to the touch, and you might be able to feel it on either side of your child's abdomen.

Wilms' tumor may also go undetected early on, because the tumors can grow large without causing pain. Your child may appear healthy or may have:

• An abdominal mass
• Fever
• Blood in the urine
• Reduced appetite
• Weight loss
• High blood pressure
• Constipation
• Stomach pain
• Nausea
• Vomiting
• General discomfort (malaise)

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Kidneys

Wilms' tumor affects the kidneys, two bean-shaped organs near the middle of your back that cleanse your blood and maintain normal levels of water and electrolytes — minerals such as sodium and potassium — in your body.

Blood travels through the renal arteries to your kidneys, which filter out waste products, unneeded electrolytes and extra water, which are then sent out of your body as urine. Urine leaves the kidneys through two tubes (ureters) and flows to the bladder. Urine leaves the bladder through a narrow tube called the urethra.

Problem arises early
In Wilms' tumor, doctors believe the cancer arises when your child is still developing in the womb. Some cells destined to form the kidneys fail to develop. Instead, they multiply in their primitive state, becoming a tumor. The tumor usually becomes evident between ages 1 and 5. The mass often distorts the kidney and can compress normal tissue into a thin rim. It may cause bleeding in the kidneys and urethra, making the urine bloody.

Most cancers occur after damage to genes. Genes program cells to develop, grow, mature and die. Cancer results when changes (mutations) arise in your genes that control growth, allowing cells to multiply without restraint. In some cases, genetic defects pass from parent to child.

Some cases of Wilms' tumor are related to defects in one of two genes — either Wilms' tumor 1 (WT1) or Wilms' tumor 2 (WT2). WT1 appears to be critical to the development of the genitals and urinary system. Scientists believe that mutations in other chromosomes also may play a role in Wilms' tumor.

Wilms' tumor occurs more frequently in children with certain abnormalities present at birth, including:

• Aniridia. In this rare condition the iris — the membrane that gives the eye its color and controls the amount of light entering the eye — forms only partially or not at all.
• Hemihypertrophy. This abnormality occurs when one side of the body is noticeably larger than the other side.

Other abnormalities are related to the genitals and urinary system, including:

• Undescended testicles. One or both testicles fail to descend into the scrotum (cryptorchidism).
• Hypospadias. The urinary (urethral) opening is not at the tip of the penis, but is on the underside.

Wilms' tumor can occur as part of rare syndromes, including:

• WAGR syndrome. This syndrome includes Wilms' tumor, aniridia, abnormalities of the genitals and urinary system, and mental retardation.
• Denys-Drash syndrome. This syndrome includes Wilms' tumor, kidney disease and male pseudohermaphroditism, in which a boy is born with undeveloped genitalia and undescended testicles.
• Beckwith-Wiedemann syndrome. Symptoms of this syndrome are omphalocele — the abdomen fails to close around the base of the umbilical cord and abdominal organs protrude into the base of the cord — a large tongue (macroglossia), and enlarged internal organs.

Take your child to the doctor if you detect an abdominal mass or if you notice blood in the urine. There may be other signs and symptoms, such as fever, high blood pressure, constipation, reduced appetite, abdominal pain and weight loss. These symptoms may not be associated with Wilms' tumor, but see your child's doctor to evaluate them.

If your child has been treated for Wilms' tumor, report any new signs or symptoms to your child's doctor. These problems may be a sign of cancer returning or of side effects of treatment.

Your child's doctor will ask about signs and symptoms, other medical problems, and the mother's pregnancy. It's also helpful to know if there's a family history of cancer or congenital defects, particularly those of the genitals and urinary system.

Your child's doctor will perform a physical examination and order laboratory tests of blood and urine. Imaging tests are essential to help locate the tumor. They include:

• Ultrasound. This noninvasive technique uses sound waves to create images of organs.
• Computerized tomography (CT). This imaging method uses X-rays to produce detailed, cross-sectional images of the body.
• Magnetic resonance imaging (MRI). This approach uses a magnetic field and radio waves to create cross-sectional images of the body.

Your child's doctor may order a chest X-ray, chest CT scan, chest MRI and bone scan to determine whether the cancer has spread beyond the kidneys.

Staging
With this information, your child's doctors can assess the extent (stage) of the cancer. Staging helps guide treatment decisions. The various stages of Wilms' tumor are:

• Stage I. The cancer is found only in the kidney.
• Stage II. The cancer has spread to the tissues and structures near the kidney, such as fat or blood vessels, but it can be completely removed by surgery.
• Stage III. The cancer has spread beyond the kidney area to nearby lymph nodes or other structures within the abdomen, and it can't be completely removed by surgery.
• Stage IV. The cancer has spread to distant structures, such as the lungs, liver or brain.
• Stage V. Cancer cells are in both kidneys.

Standard treatment for Wilms' tumor is surgery and chemotherapy. The stage of the tumor and appearance of the cancer cells under a microscope help determine whether your child also needs radiation therapy.

Surgery
Surgical removal of kidney tissue is called nephrectomy. The various types of nephrectomy include:

• Simple nephrectomy. In this surgery, the surgeon removes the entire kidney. The remaining kidney can increase its capacity and take over the entire job of filtering the blood.
• Partial nephrectomy. This involves removal of the tumor and part of the kidney tissue surrounding it. It's usually performed when the other kidney is damaged or has already been removed.
• Radical nephrectomy. In this type of surgery, doctors remove the kidney and surrounding tissues. Neighboring lymph nodes also may be removed.

At surgery, your child's doctor may examine both kidneys and the abdominal cavity for evidence of cancer. Samples from the kidney, lymph nodes and any tissues that appear abnormal are removed and examined by microscope to identify cancer cells.

A doctor specializing in pathology examines your child's tumor cells under a microscope and looks for features that indicate whether the cancer is aggressive or is susceptible to chemotherapy.

Chemotherapy
Chemotherapy uses medication to kill cancer cells. It may be given by pill, intravenous (IV) line or an injection.

Chemotherapy is considered systemic because it enters the bloodstream and travels throughout the body to destroy cancer cells wherever they may occur. It affects rapidly dividing cells; thus, normal cells with fast turnover — such as hair follicles, cells in the gastrointestinal tract and bone marrow, the tissue at the core of bone that manufactures blood cells — are affected as well as cancer cells. As a result, these medications can have the side effects of nausea, vomiting, loss of appetite, hair loss and low white blood cell counts. Most side effects will improve after the drug is stopped, and some may lessen during therapy. Ask your child's doctor what side effects may occur during treatment.

At high doses, chemotherapy can destroy bone marrow. Although it's not usually standard treatment, if your child is to undergo high-dose chemotherapy, your child's doctor may suggest that marrow be removed in advance and frozen. After chemotherapy, the marrow will be returned through an IV line, a procedure called autologous bone marrow reinfusion.

Radiation therapy
Radiation therapy uses X-rays or other sources of high-energy rays to kill cancer cells. It's usually started within a few days after surgery. If your child is very young, he or she may need a sedative to remain still during treatment. A doctor specializing in radiation therapy will mark the area to be treated with a special dye. Areas that should not receive radiation are shielded. Possible side effects include nausea, fatigue and skin irritation. After treatment, be prepared to apply a sunscreen lotion to your child's skin to avoid sunburn. Diarrhea may occur after radiation to the abdomen — ask your doctor to suggest an over-the-counter or prescription medication for relief.

Treatment regimens by stage
The treatment your child undergoes depends on the stage of the cancer, the type of cancer cell (histology), and the child's age and general health.

• Stage I or II cancer. If the cancer is restricted to the kidney or nearby structures — and the cell type is not aggressive, your child will undergo removal of the affected kidney and tissues and some of the lymph nodes near the kidney, followed by chemotherapy. Some stage II cancers are also treated with radiation.
• Stage III or IV cancer. If the cancer has spread within the abdomen and can't be completely removed without jeopardizing structures such as major blood vessels — radiation will be added to surgery and chemotherapy. Your child may undergo chemotherapy before surgery to shrink the tumor.
• Stage V cancer. If the tumor cells are in both kidneys — part of the cancer from both kidneys will be removed during surgery and neighboring lymph nodes taken to see if they contain tumor cells. Chemotherapy is used to shrink the remaining tumor. Surgery is repeated to remove as much tumor as possible while leaving functioning kidney tissue. More chemotherapy and radiation therapy may follow.

Children react differently to therapies, so adjustments may be necessary. Discuss your child's treatment plan with his or her doctor and make certain that you understand the benefits and risks before giving your consent. Ask the doctor about side effects of treatments and when to report them.

Your child's prognosis depends on the stage and cell type of the tumor.

Considering a clinical trial
Your child will receive the best care at a major medical center whose staff has expertise in treating this form of cancer. Your child's regular doctor can arrange a referral.

Because advances in treating children with Wilms' tumor have come through research, you may be asked to consider letting your child participate in a clinical trial, a carefully planned study to evaluate the benefits and risks of experimental treatments. Researchers must give you all of the available information about the trial before asking you to sign consent forms. A large percentage of children with cancer are treated in a clinical trial at some point in their illness. However, enrollment in a clinical trial is up to you and your child. Talk to your child's doctor to find out more about clinical trials.

Scientists don't know how to prevent Wilms' tumor. If your child exhibits at birth one or more of the risk factors for Wilms' tumor, his or her doctor may recommend annual ultrasound exams to detect any tumor early. If you have a family history of Wilms' tumor, tell your doctor during preconception counseling.

Here are some suggestions to help you guide your family through cancer treatment:

• Bring a favorite toy or book to office or clinic visits, to keep your child occupied while waiting.
• Stay with your child during a test or treatment, if possible. Use words that he or she will understand to describe what will happen.
• Include time for play in your child's schedule. Play can be a useful outlet in the hospital. Major hospitals usually have a playroom for young patients. Often playroom staff members are part of the treatment team and have training in child development, recreation, psychology or social work. If your child must remain in his or her room, a recreational therapist or child-life worker may be available to make a bedside visit.
• Monitor your child's energy level outside of the hospital. If he or she feels well enough, gently encourage participation in regular activities. At times your child will seem tired or listless, particularly after chemotherapy or radiation, so make time for adequate rest, too.
• Keep a daily record of your child's condition at home — body temperature, energy level, sleeping patterns, drugs administered and any side effects. Share this information with your child's doctor.
• Plan a normal diet unless your child's doctor suggests otherwise. Prepare favorite foods when possible. If your child is undergoing chemotherapy, his or her appetite may dwindle. Make sure fluid intake increases to counter the decrease in solid food intake.
• Encourage good oral hygiene for your child. A mouth rinse can be helpful for sores or areas that are bleeding. Use lip balm or petroleum jelly to soothe cracked lips. Ideally, your child should have necessary dental care before treatment begins. Afterward check with your child's doctor before scheduling visits to the dentist.
• Check with the doctor before any vaccinations, because cancer treatment affects the immune system.

• Don't be alarmed if your child's development slows or regresses to a previous developmental level under the stress of illness and treatment. Your child may become fearful when you leave the hospital and may experience separation anxiety. Be reassuring that you will return.

  Explain treatment in words your child understands. For example, tell your toddler about the illness and that medicine will make it better. Your school-age child will probably realize that cancer is a serious illness. Tell him or her that treatment for Wilms' tumor is effective and that you'll provide understanding, comfort and support.

• Be prepared to talk with your other children about the illness. Tell them about changes they might see in their sibling, such as hair loss and flagging energy.
• Ask for support from clinic or hospital staff members. Seek out organizations of parents of children with cancer.