Dr. Peter Dirks is a Professor of Neurosurgery and Molecular Genetics and a Senior Scientist in the Developmental and Stem Cell Biology Program at the Hospital for Sick Children and the University of Toronto. His research focus is on the biology of brain tumours of children and adults, with a primary aim to understand how the molecular programs in normal neural stem cells become perturbed to cause and sustain the growth of these hard-to-treat cancers. In addition, he is interested in brain tumour heterogeneity and how the diverse cell types that comprise these tumours contribute to tumour maintenance and therapeutic resistance. In 2004, his laboratory was the first to prospectively identify cancer stem cells in human brain tumours, contributing to a paradigm shift in understanding solid cancer growth, and putting emphasis on consideration of stemness properties both experimentally and conceptually in the study of brain tumours. More recently, he has used lineage tracing to identify rare populations of quiescent therapy resistant stem cells that drive the growth and relapse of medulloblastoma in mice, strongly supporting a hierarchical organization of this particular tumour type and a need to target cancer stem cells, in addition to tumour bulk, to effect more durable brain tumour cures.