To the Editors:We read with interest the article by Gutierrez et al,1 who addressed the important question of whether children diagnosed with neuroblastoma or Wilms tumor treated at a high-volume center had a better survival than children treated at a low-volume center. Gutierrez et al1 defined high-volume centers as centers that cumulatively treated more than approximately 50% of patients for each diagnosis; the remainder were classified as low-volume centers. For both tumors, no statistically significant...