Wilms Tumor (Childhood Kidney Cancer)

Wilms tumor is the most common kidney cancer in children. Doctors also call it nephroblastoma. It starts in one kidney, most often in a child between 2 and 5. About 650 children in the United States get this diagnosis each year. Your child's team can explain the outlook for their stage.

Many parents notice a firm, smooth lump in the child's belly. That is often the first sign. Other signs can include blood in the urine, a fever that will not go away, less appetite, weight loss, or belly pain. Sometimes doctors find the tumor during a routine checkup, before any symptoms show up.

Doctors confirm the diagnosis with imaging tests, like an ultrasound or a CT scan. Surgery to remove the tumor also lets doctors study the tissue. That tells them the exact type of Wilms tumor your child has.

Stage tells doctors how big the tumor is and whether it has spread. There are five stages, from I to V.

• Stage I: The tumor stays inside one kidney. Surgery removes it completely.
• Stage II: The tumor has grown into blood vessels or tissue near the kidney, but surgery still removes it all.
• Stage III: Some cancer remains in the belly after surgery, or it has reached nearby lymph nodes.
• Stage IV: The cancer has spread to organs farther away, like the lungs, liver, bones, or brain.
• Stage V: Both kidneys have a tumor at diagnosis.

Doctors also check the tumor's histology — what the cancer cells look like under a microscope. Most Wilms tumors have "favorable" histology. The cells look close to normal, and the cancer usually responds well to treatment. A smaller number have "anaplastic" histology, meaning the cells look very abnormal. Anaplastic tumors need stronger treatment.

Treatment almost always starts with surgery. Doctors remove the affected kidney in an operation called a nephrectomy. They also remove nearby lymph nodes to check them for cancer cells. Most children live a full, healthy life with one working kidney.

After surgery, most children also get chemotherapy. Common drugs include vincristine, dactinomycin, and doxorubicin. The number of drugs and the length of treatment depend on the stage and the histology. Higher stages and anaplastic tumors need more chemotherapy, sometimes adding carboplatin, etoposide, cyclophosphamide, or ifosfamide.

Some children also need radiation therapy. This is more common at higher stages, or when the histology is anaplastic. Radiation can target the belly or, if the cancer has spread, the lungs or other affected areas.

When a tumor affects both kidneys (stage V), doctors usually start with chemotherapy to shrink the tumors first. They check the response with imaging around 6 to 12 weeks later. Surgery follows, and surgeons try to save as much healthy kidney tissue as possible.

A small number of children have a genetic condition that raises their risk, such as WAGR syndrome, Denys-Drash syndrome, or Beckwith-Wiedemann syndrome. Children with these conditions, or with related features like aniridia (a missing part of the iris) or hemihypertrophy (one side of the body larger than the other), usually get regular belly ultrasounds. These are often done every 3 months until around age 8, so a tumor can be caught early.

Treatment can affect the heart, lungs, kidneys, and fertility later in life. Some survivors face a higher risk of a second cancer, including leukemia or cancer of the thyroid, breast, or skin. Ask your child's team for a written survivorship care plan. It should list what to watch for and when your child needs checkups.

Call your child's care team immediately for a fever of 100.4°F or higher during chemotherapy, unusual bleeding, new or worsening pain, or trouble breathing. Chemotherapy lowers blood counts for weeks at a time, and infections can turn serious fast while counts are low.

Ask what stage and histology your child's tumor has. Ask whether radiation is part of the plan, and why. Ask what chemotherapy drugs your child will get and for how long. Ask for a written survivorship care plan for follow-up care once treatment ends.

• National Cancer Institute — Wilms Tumor and Other Childhood Kidney Tumors Treatment (PDQ).
• National Cancer Institute — Late Effects of Treatment for Childhood Cancer (PDQ).
• National Cancer Institute — Infections in People with Cancer.