Flow cytometric detection of MRD is based on the principle that ALL cells express immunophenotypic features that can be used to distinguish them from normal hematopoietic cells, including hematogones and activated lymphocytes commonly referred to as Leukemia associated immunophenotype (LAIP). In virtually all patients with ALL, leukemia-associated immunophenotypes can be deﬁned at diagnosis and then used to monitor MRD during treatment.