How is Wilms tumor staged?

Staging is the process of finding out how far a cancer has spread. Your child's treatment and prognosis (outlook) depend, to a large extent, on the cancer's stage. Staging is based on the results of the physical exam and imaging tests (ultrasound, CT scans, etc.), which were described in "How is Wilms tumor diagnosed?", as well as on the results of surgery, if it has been done.

National Wilms Tumor Study Group (NWTSG) staging system

A staging system is a standard 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 contained within one 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 before 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 before 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 (belly). One or more of the following features may be present:

• The cancer has 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 sample removed by surgery, indicating that some of the cancer still remains after surgery.
• The cancer "spilled" into the abdominal cavity 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 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, brain, 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 diagnosis.

About 5% of all Wilms tumors are stage V.