Background: Positivity for myeloperoxidase is considered the diagnostic hallmark of myeloid lineage and is the major criterion in the classification of acute leukemias. Early myeloid precursors, however, may be cytochemically negative for myeloperoxidase enzymatic activity or protein, but positive for myeloperoxidase mRNA.
Objective: To evaluate the expression of the myeloperoxidase gene in leukemic blasts at the mRNA level and correlate the expression with blast cytochemistry and immunophenotyping.
Patients and methods: Sixteen cases of acute myelogenous leukemia and six cases of acute lymphoblastic leukemia were studied retrospectively using cellular material from Wright-stained and unstained archival smears of peripheral blood and bone marrow aspirate and a reverse-transcription polymerase chain reaction procedure for detection of myeloperoxidase mRNA.
Results: Positivity in leukemic blasts was found in all acute myelogenous leukemia cases, including cases of M0, M1, and M5 that were cytochemically negative, equivocal, or weakly positive for the enzyme. None of the acute lymphoblastic leukemia cases showed positivity for myeloperoxidase mRNA.
Conclusions: The procedure is a highly specific and sensitive method for diagnosis of myeloid lineage in leukemic blasts.