Wilms’ tumors are classified as favorable and unfavorable. These distinctions tell us how challenging the tumor may be to treat. About 90 percent of children with Wilms’ tumor have favorable tumors. That means the cells look relatively normal under the microscope and the disease can be more easily cured. Unfavorable cells appear deformed, also known as anaplastic. These are more difficult to treat. In addition to how the tumor looks under a microscope, we also look at its chromosomes — changes in certain chromosomes can show us that the tumor is harder to treat.

Staging is a measure of how far the tumor has spread. It helps our doctors determine the best treatment for your child. There are five stages of Wilms’ tumor:

• Stage 1: The cancer is only in one kidney and can be completely removed through surgery. Sometimes, children with stage I Wilms’ tumor do not need any treatment beyond surgery. 
• Stage 2: The cancer has spread to areas around the kidney and can be completely removed through surgery.
• Stage 3: The cancer has spread to areas near the kidney, such as the lymph nodes, and cannot be completely removed through surgery.
• Stage 4: The cancer has spread to organs such as the lungs, liver, bone, or brain.
• Stage 5: Tumors are found in both kidneys. Each kidney is staged separately.