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Risk Groups

To assign the best treatment to your child, your child's doctor will determine which risk group your child belongs to depending on:

The appearance of Wilms 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)

Favorable Wilms tumor

A Wilms tumor can have a favorable appearance when looking under the microscope. This means that the cells of this tumor look more like normal kidney cells. This type of Wilms tumor makes up about 90% of the cases, and usually responds well to treatment.

Unfavorable Wilms tumor (Anaplastic Wilms tumor)

A Wilms tumor can have an unfavorable (anaplastic) appearance when looking into the microscope. The cells are very different from normal kidney cells; some being very large and the cells divide more rapidly. Anaplastic changes can be either focal or diffuse.

  • Focal anaplasia: Anaplastic changes are confined to a small region within the tumor.
  • Diffuse anaplasia: Anaplastic changes are present in multiple sites within the tumor or in the tissue outside of the kidney. The presence of anaplasia in a biopsy is also considered diffuse anaplasia.

Wilms tumor with unfavorable histology does not respond as well to treatment as Wilms tumor with favorable histology. Although, tumors with focal anaplasia have a better prognosis than tumors with diffuse anaplasia.

Staging of Wilms Tumor

Staging is a process that determines how widespread the cancer may be. The stage tells the doctor if the cancer has spread and if so, how far it has spread. To assign a stage to your child's tumor, his or her doctor will use the information from imaging studies, the report from the pathologist who looked at the tumor under the microscope, and the observations about the tumor which were concluded by the surgeons when the tumor was removed. Staging systems change over time. The staging system below is the current staging system used by the Children's Oncology Group.

  • Stage I: The tumor is present only in the kidney and has been completely removed. No biopsy of the tumor was performed.
  • Stage II: The tumor has grown past the kidneys to nearby areas, but was completely removed. Examples of spread are when the tumor has grown beyond the outside covering of the kidney or has grown into blood vessels.
  • Stage III: The tumor could not be completely removed by the surgeon at diagnosis, or the tumor was biopsied prior to removal. It could also be because the tumor has spilled into the abdomen, or the tumor has spread into nearby lymph nodes.
  • Stage IV: The tumor has spread through the bloodstream to the lungs, liver, bone, lymph nodes, or brain. The most common sites of spread are the lungs (80%) and liver (15%).
  • Stage V: The tumor is present in both kidneys at the time of diagnosis. Each kidney is staged separately using the above criteria as stage I, II, III.

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.

Test results from the molecular biology studies (If your child participates in a clinical trial)

LOH (Loss of Heterozygosity)

Recent research has focused on identifying important markers that help doctors to select the best treatment for each child. The last phase III clinical trial (NWTS-5) by the Children's Oncology Group identified the loss of markers on chromosome 16q and 1p. This loss of markers is called LOH (Loss of Heterozygosity).

Children who have LOH have a slightly higher risk for their tumor to come back. If your child was identified to have LOH, they 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 without LOH.

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