1 Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands.
2 Department of Pathology, Princess Máxima Center for Pediatric Oncology, Utrecht, The Netherlands.
3 University Medical Center Utrecht, Utrecht, The Netherlands.
4 Developmental Biology and Cancer Programme, UCL Great Ormond Street Institute of Child Health and Department of Histopathology, Great Ormond Street Hospital for Children, NHS Foundation Trust, London, UK.