In BCR-ABL-positive acute lymphoblastic leukemia (ALL) and advanced stages of chronic myeloid leukemia (CML; accelerated phase, blast crisis (BC)) central nervous system (CNS) involvement is a lethal complication, typically occurring late in the course of the disease, particularly after allogeneic stem cell transplantation (alloSCT). Here, ABL1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.