1. Deptartment of Surgery and Urology for Children and Adolescents Medical University of Gdansk Gdansk Poland
2. Department of Pediatric Hematology Oncology and Immunology Olgahospital, Klinikum Stuttgart Germany
3. Department of Pediatric Pathology University Hospital of Schleswig‐Holstein Kiel Germany
4. Department of Pediatrics Hematology and Oncology Medical University of Gdansk Gdansk Poland
5. Department of Bone Marrow Transplantation Children Oncology and Haematology Medical University of Wroclaw Wroclaw Poland
6. Department of Pediatric Oncology Children's Memorial Health Institute Warsaw Poland
7. Department of Pediatric Surgery and Organ Transplantation Children's Memorial Health Institute Warsaw Poland
8. Department of Pediatric Surgery and Pediatric Urology University Children's Hospital Tuebingen Germany