BMI1 and acute lymphoblastic leukemia: To further detect the expression level of Bmi-1 in different clinical risk grade groups, all patients were divided into three hierarchy subgroups (LR, IR, and HR) according to their clinical information (e.g., patient age, initial leukocyte count, chromosomal aberrations, immunophenotype, minimal residual disease and responsiveness to chemotherapy) as described in Yeoh AE et al. [33] and the CCLG-ALL-2008 protocol [34].