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Age distribution of Wilms' tumor: report from the National Wilms' Tumor Study.

Median ages at diagnosis were 36.5 and 42.5 mo for 1523 males and 1678 females with unilateral Wilms' tumor registered between October 1969 and December 1985; they were 23.5 mo and 30.5 mo for 100 males and 141 females with bilateral disease. The median age for multicentric, unilateral cases was intermediate between the bilateral and unicentric medians. Patients with hemihypertrophy in addition to their Wilms' tumor had a typical age distribution, whereas those with aniridia or characteristic genitourinary anomalies were substantially younger. Patients with perilobar nephroblastomatosis had a median age of 35.5 mo and those with intralobar nephroblastomatosis, a median age of 18.5 mo. Most of the bilateral disease occurred in the presence of one or both of these precursor lesions. These findings suggest heterogeneity in the pathogenesis of Wilms' tumor, having implications for genetic counselling, and call into question certain aspects of Knudson and Strong's two-stage mutational model for the origin of Wilms' tumor.