Wilms' tumor is a rare kidney cancer that primarily affects children. Also known as nephroblastoma, Wilms' tumor is the most common cancer of the kidneys in children. Wilms' tumor most often affects children ages 3 to 4 and becomes much less common after age 5.
Wilms' tumor most often occurs in just one kidney, though it can sometimes be found in both kidneys at the same time.
Improvements in the diagnosis and treatment of Wilms' tumor have improved the prognosis for children with this disease. The outlook for most children with Wilms' tumor is very good.