1 INTRODUCTION Although nephroblastoma or Wilms tumor (WT) is rare, it is the most common childhood kidney tumor and can even seldomly arise in extra-renal sites without any association to the kidney.1 For more than 50 years this tumor has been treated in prospective multicenter and randomized trials by the International Society of Pediatric Oncology (SIOP), the Childrens' Oncology Group (COG), and others.2, 3 Outcome has improved over time with a long-term survival of 90% today.4, 5 The...