AFF1 and central nervous system leukemia: Specifically, MLL/AF4, MLL/ENL, MLL/AF9, MLL/ELL, MLL/AF6, and MLL/AF10 are the common fusion genes.[15] It has been confirmed in some studies that, leukemia with MLL rearrangement is characterized by the clinical, hematological, and prognostic features, such as the high peripheral white blood cell count, common organ infiltration, frequent central nervous system leukemia, mild mitigation through routine chemotherapy, high recurrence rate after remission, poor prognosis, short average survival time.[16] In this study, only 57 ALL children with MLL rearrangement had relatively poor prognosis.