1 Division of Childhood Cancer Epidemiology, German Childhood Cancer Registry, Institute for Medical Biostatistics, Epidemiology and Informatics, University Medical Center of the Johannes Gutenberg University, Mainz 55101, Germany. Electronic address: ronckerc@uni-mainz.de.
2 Pediatric Hematology and Oncology, Hannover Medical School, Hannover, Germany.
3 Clinical Cancer Epidemiology, The Institute of Cancer Research, London, UK.