Characteristics and outcome of patients with acute lymphocytic leukemia and myeloperoxidase-positive blasts by electron microscopy.

The purpose of the study was to analyze the clinical and laboratory characteristics of patients with acute lymphocytic leukemia (ALL) who exhibited myeloperoxidase-positive blasts by electron microscopy (EM-MPO-positive), and assess their response to therapy and their prognosis. Since 1988, 21 adults with newly-diagnosed ALL and EM-MPO-positive blasts were referred to our service. In addition to documentation of their clinical and hematopathologic characteristics, patients underwent cytogenetic, immunophenotypic, molecular, and electron-microscopic evaluations. Twenty patients were treated with the vincristine-Adriamycin-dexamethasone (VAD) regimen, and one patient was induced with amsacrine and high-dose cytosine arabinoside (ara-C). The 21 patients were among 141 patients with ALL (15%) seen during the same period. Their median age was 46 years (range 15 to 77 years). The immunophenotype was T-cell ALL in 12 patients (57%). Karyotypic studies did not demonstrate specific recurrent abnormalities. The median percentage of EM-MPO-positive blasts was 15% (range 3% to 45%). Eighteen patients (85%) had high-risk ALL. With induction chemotherapy 15 of 20 (75%) receiving VAD therapy achieved a complete remission (CR). However, the median CR duration was 18 months, and the median survival was 18 months with a 3-year disease-free survival rate of 25%. There were eight relapses and one lineage switch to acute myelogenous leukemia (AML). Patients with ALL and EM-MPO-positive disease are a unique subgroup with long-term poor prognosis on conventional anti-ALL therapy, and may benefit from intensification treatments with agents effective against AML.