Urinary system cancers are much more common in older adults than in children. For example, a condition known as Wilms tumor is the most common type of kidney cancer in children, but it affects only about 500 children a year in the United States, making it relatively rare. Bladder cancer is even more rare among children; about one tenth of one percent of the people diagnosed with bladder cancer in the United States are under the age of 20. Children may not always display the same kinds of symptoms as adults with urinary system cancers; for example, many children with Wilms tumor do not display any symptoms but often have a solid mass in their belly region that is large enough to notice when that area is touched. Aside from the potentially different symptoms, the diagnosis and treatment of urinary system cancers generally is the same in children as in adults; for example, children with Wilms tumor are treated with surgery, chemotherapy, radiation therapy, or a combination of these approaches.