Use of Myeloperoxidase mRNA in Monitoring Patients With Acute Myelogenous Leukemia for Early Detection of Circulating...

Background: Expression of the myeloperoxidase (MPO) gene is specific for myeloid precursors and their leukemic counterparts. Unlike the enzyme, MPO mRNA is found only in early myeloid precursors; this makes MPO mRNA a good marker for myeloid lineage of leukemic blasts. A reverse transcriptase-polymerase chain reaction (RT-PCR) method for MPO mRNA detection was developed and used in the diagnosis of acute myelogenous leukemia (AML). In this study, we investigated the use of MPO mRNA for early detection of circulating blasts in patients with AML during and after chemotherapy. Methods and Results: MPO mRNA detection by RT-PCR was performed on cellular material from archival smears of preipheral blood (PB) and bone marrow aspirate from 16 patients previously diagnosed with AML, types MO-M5. MPO mRNA findings were correlated with morphology and flow-cytometric data. A group of six patients diagnosed with adult de novo acute lymphoblastic leukemia served as a negative patient control group for this retrospective study. MPO mRNA findings in PB appear to follow two patterns in patients with complete remission: (1) sustained positivity throughout the clinical course, correlated with relapse; and (2) initial positivity followed by sustained negativity, correlated with long complete remissions. For the only patient in this study found in partial remission, MP mRNA positivity in PB was seen throughout the clinical course. No MPO mRNA positivity was detected in the PB of acute lymphoblastic leukemia cases. Conclusions: A highly sensitive method for detection of MPO mRNA, such as RT-PCR, is useful in monitoring patients with AML for confirming or ruling out complete remission at the molecular level. The pattern of MPO mRNA positivity over time appears to be important and to correlate with clinical course, with sustained positivity being associated wtih impending relapse, while a switch from initial positivity to sustained negativity appears to be associated with long complete remssion. Studies of larger patient groups are necessary to confirm these initial findings.