1. Department of Pediatrics, Hemato-Oncology and Gastroenterology, Pomeranian Medical University, Unii Lubelskiej 1, 71-252 Szczecin, Poland
2. Department of Pediatric, Hematology, Oncology and BMT, Wrocław Medical University, 50-367 Wroclaw, Poland
3. Department of Pediatric Hematology, Oncology and Transplantology, Medical University of Lublin, 20-059 Lublin, Poland
4. Department of Pediatric Hematology and Oncology, Silesian Medical University, 40-055 Zabrze, Poland
5. Department of Pediatrics, Hematology and Oncology, Medical University, 80-210 Gdansk, Poland
6. Department of Pediatric Hematology and Oncology, Medical University, 02-091 Warszawa, Poland
7. Department of Pediatric Oncology and Hematology, University Children’s Hospital, Collegium Medicum Jagiellonian University, 31-008 Krakow, Poland
8. Department of Pediatric Oncology, Hematology and Transplantology, University of Medical Sciences, 61-701 Poznan, Poland
9. Department of Pediatrics, Hematology and Oncology, Medical University, 90-419 Lodz, Poland
10. Department of Pediatrics, Oncology an Hematology, Medical University, 15-089 Bialystok, Poland
11. Department of Pediatrics, Hematology and Oncology, Collegium Medicum in Bydgoszcz, Nicolaus Copernicus University in Torun, 87-100 Toruń, Poland
12. Biostatistics Teaching Unit, Pomeranian Medical University, 70-204 Szczecin, Poland