Wilms Tumor Stages and Risk Groups

Children’s Oncology Group (COG) staging system

A staging system is a standard way for the cancer care team to sum up the extent of the tumor.

In the United States, the Children’s Oncology Group staging system is used most often to describe the extent of spread of Wilms tumors. This system divides Wilms tumors into 5 stages, using Roman numerals I through V.

Stage I

The tumor is contained within one kidney and was removed completely by surgery. The tissue layer surrounding the kidney (the renal capsule) was not broken during surgery.

The cancer has not grown into major blood vessels, either inside the kidney or next to it. Nearby lymph nodes (bean-sized collections of immune cells) do not contain cancer. The tumor was not biopsied before surgery to remove it.

Stage II

The tumor has grown beyond the kidney (either into nearby fatty tissue or into major blood vessels inside or near the kidney) but it was removed completely by surgery without any apparent cancer left behind. Nearby lymph nodes do not contain cancer. The tumor was not biopsied before surgery.

Stage III

The Wilms tumor most likely has not been removed completely by surgery. The cancer remaining after surgery is limited to the abdomen (belly). One or more of the following features may be present:

• The cancer has spread to lymph nodes in the abdomen or pelvis, but it has not spread to more distant lymph nodes (such as those inside the chest).
• The cancer has grown into nearby vital structures, so the surgeon could not remove it completely.
• Deposits of tumor (tumor implants) are found along the inner lining of the abdominal space.
• Cancer cells are found at the edge (margin) of the sample removed by surgery. This is a sign that some of the cancer still remains after surgery.
• Cancer cells “spilled” into the abdominal space before or during surgery.
• The tumor was removed in more than one piece. For example, the tumor was in the kidney and in the nearby adrenal gland, which was removed separately.
• A biopsy of the tumor was done before the tumor was removed with surgery.

Stage IV

The cancer has spread through the blood to organs away from the kidneys, such as the lungs, liver, brain, or bones. Or it has spread to lymph nodes far away from the kidneys.

Stage V

Tumors are found in both kidneys at the time of diagnosis.

Tumor histology

A Wilms tumor’s histology is the other main factor doctors use to determine the prognosis (outlook) and best treatment. Tumor histology is based on how the tumor cells look under a microscope.

The histology can be either favorable or anaplastic. These are described in more detail in What Are Wilms Tumors?

To learn more about how the stage and histology of a Wilms tumor might affect prognosis, see Survival Rates for Wilms Tumors.

Wilms tumor risk groups

When deciding which treatment options are best, doctors often divide children into risk groups (such as very low, low, standard, and higher). This is especially the case in clinical trials, which is how most children with Wilms tumors are treated.

These risk groups help ensure a child gets the treatment that is most likely to result in a good outcome, while limiting the chances of side effects as much as possible.

The risk groups are based on things like:

• The stage of the cancer
• The histology of the tumor
• The child’s age
• The size (weight) of the tumor
• If the tumor cells have any high-risk gene or chromosome changes

Risk groups might be assigned at different times. For example, a risk group is typically assigned before starting treatment, and then again after treatment has begun (and more has been learned about the tumor).

Talk to your cancer care team to learn more about which risk group your child falls into and what this might mean for their treatment.