B cell acute lymphoblastic leukemia is the most common cancer of childhood and remains one of the most deadly since despite improvements in outcomes, relapse remains a challenge and about only half of children suffering relapse will survive. We are using the knowledge of the normal process of development of healthy B cells to show us how B cell ALL goes wrong. These studies help us to better understand the biology of ALL cells and lead us to new approaches for risk prediction and treatment for kids with ALL. We are investigating how developmental features align with relapse sites with a special focus on the central nervous system.