National Wilms Tumor Study Group (NWTSG) staging system

A staging system is a way for the cancer care team to summarize their findings of how extensive the tumor is. The National Wilms Tumor Study Group staging system is used to describe the extent of spread of Wilms tumors. This system describes Wilms tumor stages using Roman numerals I through V (1 through 5).

Stage I

The tumor was only in the kidney and was completely removed by surgery. The tissue layer surrounding the kidney (the renal capsule) was not broken during surgery. The cancer had not grown into blood vessels in or next to the kidney. The tumor was not biopsied prior to surgery.

About 40% to 45% of all Wilms tumors are stage I.

Stage II

The tumor grew beyond the kidney, either into nearby fatty tissue or into blood vessels in or near the kidney, but it was completely removed surgically without any apparent cancer left behind. The tumor was not biopsied prior to surgery.

About 20% to 25% of all Wilms tumors are stage II.

Stage III

This stage refers to Wilms tumors that may not have been completely removed. The cancer remaining after surgery is limited to the abdomen. One or several of the following features may be present:

• The cancer is found to have spread to lymph nodes in the abdomen or pelvis but not to more distant lymph nodes, such as those inside the chest.
• The cancer has invaded nearby vital structures so the surgeon could not completely remove it.
• Deposits of tumor (tumor implants) are found along the lining of the abdominal cavity.
• The cancer cells are present at the edge of the tissue removed by surgery, indicating that some of the cancer still remains after surgery.
• The cancer "spilled" into the abdominal cavity before or during surgery.
• A biopsy of the tumor was done before it was removed.

About 20% to 25% of all Wilms tumors are stage III.

Stage IV

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

About 10% of all Wilms tumors are stage IV.

Stage V

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

About 5% of all Wilms tumors are stage V.

Survival rates by stage and histology

The survival rates below are based on the results of the National Wilms Tumor Studies, which included most of the children treated in the United States in the last few decades. The 2 most important factors in determining a child's outlook are the stage and histology of the tumor. (The histology refers to how it appears under the microscope -- see "What Is Wilms Tumor?")

Survival statistics can be complex, and there are some important points to note about these numbers:

• The survival rate refers to the percentage of children who live at least a certain number of years after being diagnosed. They are used to produce a standard way of discussing prognosis (outlook). Of course, many children live much longer than this.

• The numbers below are among the most current we have available, but they are based on children who were first diagnosed and treated many years ago. Improvements in treatment since then mean that the survival rates for those now being diagnosed with these cancers may be higher.

• Some of these numbers are based on only a small number of cases, so their accuracy is not certain.

• While survival statistics can sometimes be useful as a general guide, they may not accurately represent any one child's prognosis. Other factors, such as changes in certain chromosomes in tumor cells, may also affect outlook. Your child's doctor is likely to be a good source as to whether these numbers may apply to your child, as he or she is familiar with the aspects of the particular situation.

Wilms Tumor 4-year Survival Rates