Residual disease detected by multidimensional flow cytometry shows prognostic significance in childhood acute myeloid leukemia with intermediate cytogenetics and negative FLT3-ITD: a report from the Tokyo Children's Cancer Study Group.

Residual disease (RD) after induction chemotherapy may predict clinical outcome in acute myeloid leukemia (AML). In the present study, we investigated the prognostic significance of RD detected by multidimensional flow cytometry (MDF) among 34 children treated for AML in a clinical trial (JPLSG AML-05) in Japan. Bone marrow samples were analyzed at the points of the end of the first induction course (BMA-1) and second induction course (BMA-2) by MDF. RD was evaluated by detecting the immature cells showing abnormal antigen expression pattern; CD34+, CD15+, CD7+. Thirteen (39.4 %) of 34 patients at BMA-1 and 8 (27.6 %) of 34 at BMA-2 had RD levels ≥0.1 %. There was no significant difference in 3y-EFS and 3y-OS between patients with RD levels ≥0.1 % and those with RD levels <0.1 % (53.8 versus 70.0 %, P = 0.30 and 50.0 versus 66.7 %, P = 0.27, respectively). However, IR cytogenetics and negative FLT3-ITD patients with RD levels ≥0.1 % exhibited significantly lower 3y-EFS and 3y-OS than those with RD levels <0.1 % (33.3 versus 83.3 %, P = 0.02 and 20.0 versus 76.9 %, P = 0.005, respectively). Our study suggests that RD shows prognostic relevance in pediatric patients with IR cytogenetics and negative FLT3-ITD AML.