Clinico-Biological Characteristics and Prognosis of Non-M3 Acute Myeloid Leukemia with High Percentage of Myeloperoxisase Positive Blasts. Single Center Experience.

Introduction: It has been suggested that acute myeloid leukemia (AML) showing mature phenotype is associated with favourable outcome. In a study recently published by JALSG, myeloperoxidase (MPO) positivity in over 50% of blasts had favourable prognostic impact, independent from karyotype, on achieving complete remission (CR), overall survival (OS) and disease free survival (DFS). No other studies have established the independent prognostic value of MPO expression.

Objectives: Analyze the clinico-biological characteristics of AML with high percentage of MPO+ blasts and its impact on CR, OS and DFS.

Material and methods: Between 1986 and 2005, 418 adult patients (median 53 years, range 15–80) were diagnosed with de novo non-APL AML and evaluated for percentage of MPO+ blasts. All patients received intensive chemotherapy. Diagnosis was made by optic microscopy of bone marrow (BM) aspirates stained with May-Grumwald giemsa, MPO, butyrate esterase and or non specific esterase. Cytogenetic and immunophenotype analysis was evaluated in 66% and in 76% of the cases respectively.

Results: 118 patients (28%) showed a percentage of MPO+ blasts >75%. AML with MPO+ blasts >75% was associated with M1-M2-M4 subtypes, leucocytes >50×10⁹/L, blasts in BM >70% and HLA-DR negativity (p<0.01). It was also significantly associated with favourable karyotype (11% vs 3% favourable, 52% vs 48% intermediate and 3% vs 15% unfavourable). Patients with AML and MPO+ blasts >75% obtained higher CR rate (71% vs 55%), due to less resistant disease (9% vs 22%, p<0.01). In multivariate analysis favourable karyotype, leukocytes <50×10⁹/L and age <60 were favourable prognostic factors for CR. Median OS and DFS was higher in patients with AML and MPO+ blasts >75% (15 vs 7 months, p<0.001, y 41 vs 12 months, p<0.001, respectively). ). In multivariate analysis, favourable karyotype, leukocytes <50×10⁹/L, age <60 years and MPO+ >50% were favourable prognostic factors for OS; and age <60 and MPO+ >75% were the only independent factors for DFS. Median DFS was higher in patients with AML and MPO+ blasts >75% in the intermediate cytogenetic risk group (59 vs 13 months, p=0.015), age <60 (109 vs 15 months, p=0.003), age >60 (13 vs 7 months, p=0.03), autologous stem cell transplantation (100 vs 9 months, p=0.04) and chemotherapy alone (16 vs 8 months, p=0.003).

Conclusion: In our series, patients with AML and MPO+ blasts >75% show less chemoresistant disease and a longer remission duration, the latter independently from the karyotype. This biological characteristic could be useful in designing therapeutic strategies in patients that lack other prognostic markers.