Prognostic significance of myeloperoxidase expression in childhood acute myeloid leukemia.

BACKGROUND: The percentage of myeloperoxidase (MPO)-positive blast cells is associated with prognosis in adult acute myeloid leukemia (AML), but this association is unsubstantiated in pediatric AML. PROCEDURE: We retrospectively compared cytochemical MPO results with outcome in 154 patients younger than 21 years treated on three consecutive institutional protocols for newly diagnosed AML (1987-2001). Patients with FAB M0 and M7 AML (no MPO expression) or M3 AML (100% MPO expression) and Down's syndrome were excluded. RESULTS: Median MPO expression was higher in FAB M2 subtype than in other subtypes (P < 0.0001) and differed significantly across cytogenetic risk groups (P = 0.002) with highest MPO expression among those with favorable karyotypes. The percentage of MPO-positive blasts was not significantly associated with the probability of complete remission (P = 0.97), event-free survival (P = 0.72), or survival (P = 0.76) in multivariate analyses that accounted for age, FAB subtype, presenting WBC count, cytogenetic and protocol treatment risk group. In analysis limited to patients with intermediate-risk cytogenetics, higher MPO expression appeared to be associated with improved EFS (P = 0.06) but was not associated with remission induction rate (P = 0.16) or overall survival (P = 0.38). CONCLUSIONS: The percentage of MPO-positive blast cells is related to FAB subtype in pediatric AML but has limited prognostic relevance.