DefinitionWilms tumor is a type of kidney cancer that occurs in children.Alternative NamesNephroblastoma; Kidney tumorCauses, incidence, and risk factorsWilms tumor is the most common form of childhood kidney cancer. The exact cause of this tumor in most children is unknown.A missing iris of the eye (aniridia) is a birth defect that is sometimes associated with Wilms tumor. Other birth defects linked to this type of kidney cancer include certain urinary tract problems and enlargement of one side of the body, a condition called hemihypertrophy.It is more common among some siblings and twins, which suggests a possible genetic cause.The disease occurs in about 1 out of 200,000 to 250,000 children. It usually strikes when a child is about 3 years old. It rarely develops after age 8.SymptomsAbd