Cytochemically myeloperoxidase positive childhood acute leukemia with lymphoblastic morphology treated as lymphoblastic leukemia

Cytochemical myeloperoxidase (MPO) positivity represents the gold standard for discrimination between lymphatic and myeloid blasts. Rarely, cytochemical MPO reaction may be positive in >or=3% of blasts with clear lymphoblastic morphology. We present 5 patients with cytochemically MPO-positive acute leukemia classified as lymphoblastic by cytomorphology and lymphoblastic (n=3) or biphenotypic (n=2) by immunophenotyping, who entered first-line treatment for lymphoblastic leukemia. The former 3 are in first remission and both with biphenotypic leukemia relapsed with acute myeloid leukemia. The study primarily shows that cytochemical MPO expression in childhood acute leukemia revealing typical lymphoblastic morphology and phenotype does rarely exist. Although a small number of patients studied, cytochemical MPO expression in acute leukemia does not seem to require myeloid leukemia treatment in case of otherwise lymphoblastic cytomorphology and phenotype.