CD99 expression in acute myeloid leukemia with FLT3 internal tandem duplications (FLT3-ITDmut -AML): a flow-cytometric marker for an accurate diagnostic workup

Internal tandem duplications of FLT3 (FLT3-ITD) in acute myeloid leukemia (AML) are associated with poor outcomes. CD99 is frequently overexpressed in AML and emerged as potential diagnostic marker. Ninety consecutive newly diagnosed AML patients were retrospectively analyzed. Immunophenotypic profiles were correlated with molecular assessment. Patients were categorized into FLT3-ITDmut (28.9%) and FLT3wt (71.1%). CD99 was expressed in 100% of FLT3-ITDmut-AML compared to 48% in FLT3wt cases. FLT3-ITDmut-AML exhibited higher CD99 expression percentage. CD34 expression was lower in FLT3-ITDmut-AML, with a positivity rate of 31% versus 83% in FLT3wt cases. Multivariate analysis confirmed that CD99 positivity (OR 17.67; p = 0.010) and CD34 negativity (OR 10.00; p = 0.039) were independently associated with FLT3-ITDmut-AML. CD99 and CD34 displayed NPVs of 100% and 86.9%, respectively, with moderate PPVs (45.6% and 62.1%) for the diagnosis of FLT3-ITDmut-AML. CD99 is a highly reliable marker in FLT3-ITDmut-AML and its absence virtually excludes the presence of a FLT3-ITD mutation.