Myeloperoxidase immunoreactivity in adult acute lymphoblastic leukemia

To evaluate the frequency and significance of myeloperoxidase positivity in adult acute lymphoblastic leukemia (ALL), bone marrow biopsy material from 82 adults with ALL was evaluated with a polyclonal myeloperoxidase (pMPO) antibody. Nineteen cases (23%) demonstrated evidence of pMPO immunoreactivi ty. Positive cases were precursor B-cell lineage, and CD13 or CD15 expressi on was more frequent than in the pMPO-negative cases. A subset of pMPO;posi tive cases studied with a monoclonal MPO antibody was negative. Western blo t analysis using the pMPO antibody showed the expected 55-kd band for myelo peroxidase in pMPO-positive and pMPO-negative ALLs, suggesting a lack of sp ecificity of this antibody in ALL. Forty-two percent (8/19) of the pMPO-pos itive ALL cases demonstrated evidence of t(9;22) by either karyotype or pol ymerase chain reaction analysis. The pMPO-positive ALLs had a Lower frequen cy of extramedullary disease than the pMPO-negative group and a trend towar d improved overall survival compared with the pMPO-negative group. Immunore activity with pMPO in adult ALL may lend to an incorrect interpretation of biphenotypic acute leukemia using a recently described scoring system, mid a revision to that scoring system is proposed to accommodate pMPO-positive ALL.