Clinical characteristics
AML-M2 was the most common phenotype, which occurred in 82.7% (62/75) of children and 92.9% (91/98) of adults (P=0.005). Thirty nine patients (22.5%) presented with various forms of EML, including central nervous system leukemia (CNSL) (n=12), sarcoma within or beside the spine (n=17), and others (n=10). Compared to adult group, the pediatric cohort had a much lower incidence of EML (children 10/75, 13.3% vs. adults 29/98, 29.6%, P=0.011). Of the 39 patients with EML, there were 1 child (1/10, 10.0%) vs. 14 adults (14/29, 48.3%, P=0.032) presenting with sarcoma within or beside the spine (Table 2). C-KIT mutations were also less frequently observed in children (12/68, 17.6%) than in adults (30/74, 40.5%, P=0.003). Otherwise, there were no statistical differences with regards to gender, peripheral white blood cell count (WBC), immunphenotype of CD34, CD13, CD33, CD117, HLA-DR, CD19 and CD56 positive expression, cytogenetic abnormality, and gene mutations including FLT3-ITD and NPM1 between the two age groups (Table 1).