MYELOPEROXIDASE MESSENGER-RNA ANALYSIS IN ACUTE LYMPHOBLASTIC-LEUKEMIA

Expression of the myeloperoxidase (MPO) gene at the mRNA level is a be tter lineage marker than enzymatic activity in early myeloid precursor s and their leukemic counterparts. Its diagnostic use depends on the s pecificity of expression for myeloblasts and its absence in blasts of lymphoid lineage. The present study investigates MPO mRNA expression i n adult acute lymphoblastic leukemia (ALL), using reverse transcriptio n-polymerase chain reaction. Of a total of 13 cases, six were found to have blasts positive for MPO mRNA; in all of these cases, the blasts were cytochemically negative for MPO. This unexpected finding of MPO m RNA positivity in six of 13 cases was further investigated at the mole cular level. Bcr gene rearrangement analysis was positive in all six c ases for the bcr breakpoint diagnostic of chronic myelogenous leukemia (CML). Only three of these six cases were cytogenetically positive fo r a Philadelphia (Ph) chromosome. Based on molecular analysis, these c ases are considered as CML presenting in blast crisis of lymphoid line age, as opposed to de novo ALL. The remaining seven cases were Ph nega tive at the cytogenetic and molecular levels; the leukemic blasts were MPO mRNA negative, confirming the lack of MPO gene expression in de n ovo ALL.