Wilms’ tumor is a rare kidney cancer that primarily affects children. Also known as nephroblastoma, it’s 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.Over the years, advancements in the diagnosis and treatment of Wilms’ tumor have greatly improved the outlook (prognosis) for children with this disease. With appropriate treatment, the outlook for most children with Wilms’ tumor is very good. (source)