Else Driehuis1,2,3, Kai Kretzschmar4,5, Hans Clevers6,7. 1. Oncode Institute, Hubrecht Institute, Royal Netherlands Academy of Arts and Sciences (KNAW) and University Medical Center (UMC) Utrecht, Utrecht, the Netherlands. 2. Hubrecht Organoid Technology (HUB), Utrecht, the Netherlands. 3. Department of Pathology, University Medical Center (UMC) Utrecht, Utrecht, the Netherlands. 4. Oncode Institute, Hubrecht Institute, Royal Netherlands Academy of Arts and Sciences (KNAW) and University Medical Center (UMC) Utrecht, Utrecht, the Netherlands. kai.kretzschmar@uni-wuerzburg.de. 5. Mildred-Scheel Early Career Centre (MSNZ) for Cancer Research, University Hospital Würzburg, Würzburg, Germany. kai.kretzschmar@uni-wuerzburg.de. 6. Oncode Institute, Hubrecht Institute, Royal Netherlands Academy of Arts and Sciences (KNAW) and University Medical Center (UMC) Utrecht, Utrecht, the Netherlands. h.clevers@hubrecht.eu. 7. Princess Máxima Center for Pediatric Oncology, Utrecht, the Netherlands. h.clevers@hubrecht.eu.