Wilms tumor is the most common renal malignancy in children and the fourth most common childhood cancer . The epidemiology, presentation, diagnosis, and staging of Wilms tumor will be reviewed here. The treatment and outcome of Wilms tumor are discussed separately. (See "Treatment and prognosis of Wilms tumor".)
In the United States, the annual incidence of renal tumors is about eight cases per million children younger than 15 years , accounting for 7 percent of all childhood malignancies  and for 500 new cases per year in North America [1,3-6]. Wilms tumor is the most common renal malignancy in children under the age of 15 years, accounting for about 95 percent of all cases. In contrast, renal cell carcinoma is more common in the 15 to 19-year-old age group .
In the United States, two-thirds of cases of Wilms tumor are diagnosed before five years of age, and 95 percent before 10 years of age . In patients with unilateral involvement, the median age at diagnosis is 43 months in girls and 37 months in boys . Children with bilateral disease are diagnosed at an earlier age (median age, girls at 31 months and boys at 24 months) . Patients with associated congenital anomalies, such as aniridia or genitourinary abnormalities, are also diagnosed at an earlier age .
The risk of developing Wilms tumor varies among ethnic groups, with a greater risk in African-Americans and a lower risk in the Asian population [1,8,9]. Epigenetic differences may contribute to the lower rate of disease in Asian children, as demonstrated by a study that reported infrequent loss of IGF2 imprinting in tumors from Asian patients . (See 'Genetics' below.)
Associated congenital syndromes — Wilms tumor is primarily a sporadic disease, and only 1 to 2 percent of individuals with Wilms tumor have a relative with the disease . In some children, Wilms tumor occurs as a part of a multiple malformation syndrome . These syndromes include WAGR, Denys-Drash, and Beckwith-Wiedemann syndromes.