OBJECTIVEEarly response to therapy is one of the most important prognostic factors in childhood acute lymphoblastic leukemia (ALL). This study aimed to assess the prognostic value of morphological assessment of bone marrow blasts during remission induction and determination of minimal residual disease (MRD) after remission induction.

METHODSFrom January 1998 to May 2003, 193 children with newly diagnosed ALL were enrolled on the ALL-XH-99 protocol. Blast cell count in the bone marrow was examined on day 19 of remission induction and by the completion of remission induction. MRD was measured with the flow cytometry. Event-free survival (EFS) was estimated by Kaplan-Meier analysis and the distributions of EFS were compared using the log-rank test. A Cox proportional hazards model was used to identify independent prognostic factors.

RESULTSThe 4-year EFS was significantly worse in patients with > or = 5% lymphoblasts in the bone marrow on day 19 as compared to those with <5% lymphoblasts on that date (42.59%+/- 14.28% vs 74.24%+/- 6.67%; p< 0.01). The 4-year EFS was significantly worse in patients with any amount of lymphoblasts in the bone marrow on the remission date as compared to that of other patients with no morphologically identifiable blasts (63.47%+/-9.23% vs 76.41%+/- 6.09%; p<0.05). The patients with MRD <0.01 had significantly better outcome than those with a level > or = 0.01% (15-month EFS:94.44%+/-5.40% vs 23.81%+/- 20.26%; p<0.01).

CONCLUSIONSEarly treatment response as assessed by morphological examination or minimal residual leukemia determination by flow cytometry has important prognostic significance, and can be performed in a resource-poor patient population.