MD2B - Pediatric Oncology: Wilms Tumor

Overview

Wilms tumor, also known as "nephroblastoma", is a solid tumor that arises from immature kidney cells. Wilms tumor is the fourth most common type of pediatric cancer, and is the most common type of kidney cancer to occur in children. Approximately 500 new cases are diagnosed each year. Wilms tumor most frequently occurs around the age of 3, and is rarely seen after 8 years of age. It usually affects only one kidney (unilateral), but in 5% of cases can affect both kidneys (bilateral). The overall five-year survival rate for children with Wilms' tumor is more than 90%. Prognosis depends on stage (how far the cancer has spread), histopathologic features (what the cancer cells look like under the microscope), patient age, and tumor size.

Symptoms

Most Wilms tumors are found only after the tumor has become quite large because the tumors can grow for some time without causing pain or making the child appear unhealthy. Luckily however, the tumors are usually discovered before they have metastasized (spread to other organs). Most commonly, the tumor is discovered because the child's abdomen begins to swell. Often parents appreciate a hard mass in the child's belly while they are bathing or dressing their child. The tumor is not usually painful to the child. Other less common symptoms of Wilms tumor include abdominal pain, fever, hematuria (blood in the urine), nausea, vomiting, weight change, change in bowel movements, or high blood pressure observed at the pediatrician's office (due to elevated levels of a substance in the blood called renin).

Diagnosis

The child's physician will perform a physical examination, schedule imaging tests, and order laboratory tests to help determine if the child has Wilms tumor and to aid in developing the appropriate treatment plan.

Imaging tests

• Ultrasound: Ultrasonography uses sound waves to produce images of internal organs. It can tell whether a mass is cystic or solid and often can help to distinguish benign (not harmful) conditions from malignant (cancerous) tumors. This is often the first imaging study to be done because it is painless and noninvasive.
• CT/ CAT scan: CT scan uses x-rays to create cross sectional pictures of the tumor. It can often demonstrate tumor spread into adjacent organs and can often detect small tumor, if present, in the opposite kidney. As part of this test, dye will sometimes be placed through an IV into the child's veins to help make the pictures more clear.
• MRI: An MRI scan uses radio waves and strong magnets rather than x-rays to create pictures of the tumor. MRI gives more detailed images than CT and ultrasound and can help doctors see if the cancer has invaded any of the major blood vessels around the kidney.
• Additional tests to look for metastasize (spread of tumor ): chest x-ray or chest CT scan to look for cancer in the lungs, radionucleotide bone scan and x-ray skeletal surveys to look for cancer in the bones, brain MRI to look for cancer in the brain.

Lab tests

• CBC: a blood test to look at the number of each type of blood cell
• Electrolyte Panel: a blood test to measure levels of chemicals and salts in the blood. This helps evaluate the level of kidney and liver functioning. It also determines the level of calcium in the blood which can help in diagnosis
• Urinalysis: a urine test to determine blood and other substances in the urine

Staging and Prognosis

Based on physical examination, imaging studies, laboratory tests, and possibly biopsy (tissue sample) the doctor will stage the tumor according to the following categories:

Stage 1: tumor confined to only the kidney and can be completely removed by surgery

Stage 2: tumor extends beyond the kidney but can be completely removed by surgery

Stage 3: cancer has spread slightly beyond the kidney (but not outside of the abdomen and pelvis) and can not be completely removed by surgery

Stage 4: cancer has spread outside the abdomen and pelvis to other organs such as the lungs, liver, bone, or brain

Stage 5: cancer in both kidneys

Age of the patient, size of the tumor, lymph node involvement and metastases at time of diagnosis, and appearance of the cancer cells are all important prognostic factors in determining survival.

Treatment

Treatment of Wilms tumor involves combinations of surgery, chemotherapy, and possibly radiation. Due to advances in the treatment of Wilms tumor, the overall success rate in curing this type of cancer is now around 90%.

Surgery

Surgical removal is the primary method for achieving local control of the cancer. A surgeon will perform a "nephrectomy" removing part of the kidney, the whole kidney, or the kidney plus surrounding tissue depending on the location and spread of the tumor at time of diagnosis.

Chemotherapy

Chemotherapy is a systemic treatment for Wilms tumor. Chemotherapy is taken orally or IV. It travels through the bloodstream and goes throughout the entire body to kill cancer that has spread beyond the kidney. Side effects of chemotherapy include nausea and vomiting, mouth sores, change in bowel habits, loss of hair, increased risk of infection, fatigue, and bruising.

Radiation

Radiation uses high-energy rays to kill cancer cells. Radiation is used in the more advanced stages of Wilms tumor. Side effects of radiation include nausea, diarrhea, fatigue, and skin changes.

Syndromes associated with Wilms Tumor

In a small number of cases, Wilms tumor arises as part of a congenital malformation syndrome. In the WAGR syndrome which results from a mutation at chromosome 11p, children have Wilms tumor, aniridia (absence of the iris of the eye), genital-urinary malformations, and mental retardation. In Denys-Drash Syndrome which also results from a mutation at 11p, children suffer from the combination of Wilms tumor, renal (kidney) disease, and pseudo-hermpahroditism ( genitalia are of one sex, but some physical characteristics of the other sex are present ). In Beckwith-Wiedemann Syndrome, children have macroglossia (a large tongue), omphalocele (abdominal organs outside of the body), Wilms tumor, and visceromegaly (large organs). Wilms tumor has also been described in association with Bloom Syndrome, Fanconi anemia, and Li Fraumeni syndrome.