Stage I: The tumor is only in one kidney and can be completely removed by surgery. About 43 percent of patients with Wilms' tumor are stage I.

Stage II: Cancer is also found in the fat, soft tissue or blood vessels near the kidney. It may have spread to the renal sinus (part of the kidney through which blood and fluid enter and exit the organ). The growth can be completely removed by surgery. About 23 percent of patients have stage II Wilms' tumor.

Stage III: Cancer is found in areas near the kidney. It cannot be completely removed by surgery. The tumor may have spread to nearby organs and blood vessels or throughout the abdomen and to nearby lymph nodes (small bean-shaped organs that produce and store infection-fighting cells of the immune system). About 23 percent of patients have stage III Wilms' tumor.

Stage IV: Cancer has spread to organs such as the lungs, liver, bone and brain. About 10 percent of patients are in stage IV.

Stage V: Cancer cells exist in both kidneys at the same time. About 5 percent of patients have bilateral disease.