AML1/ETO Fusion Gene in de novo Pediatric Acute Myeloid Leukemia: Clinical Significance and Prognostic Implications

The characterization of leukemia-associated chromosome translocations has contributed relevant insights into our understanding of leukemia pathogenesis and has provided new specific tumor markers essential in prognostic assessment and minimal residual disease studies. The aim of this work is to study the frequency of AML1/ETO fusion gene in a series of Egyptian childhood AML cases. The clinical significance and prognostic implications of this aberration, including CR rate, duration of first CR, extramedullary leukemia (EML), and survival are investigated as well. Peripheral blood and/or bone marrow mononuclear cells were available for analysis from 78 children, all newly diagnosed with AML. AML1/ ETO fusion transcript was detected by the reverse transcriptase- polymerase chain reaction (RT-PCR) technique. Patients with de novo AML were treated by 2 courses of induction chemotherapy, followed by 4 courses of consolidation treatment if the patient achieved complete remission (CR). The marrow status was evaluated after each course in order to check bone marrow cellularity and presence of blasts. Patients with less than 5% blasts by the end of the second course of ADE passed to consolidation chemotherapy. Patients with more than 5% blasts by the end of the second course of ADE were excluded from the study. The AML1/ETO fusion transcript was detected by a singleround RT-PCR reaction and was found to be expressed in 15 out of 78 cases (19.2%). AML1/ETO positive patients were 7 girls and 8 boys, with ages ranging from 5 to 15 years. Seven cases (46.67%) belonged to FAB subtype M1, 7 (46.67%) M2, while only one case (6.67%) belonged to M5a subtype. Their total leukocytic counts ranged from 7.1 to 183.0 x 109/l with a median of 21.0 x 109/l. Their hemoglobin concentrations ranged from 4.8 to 10.3g/dl with a median of 7.4g/dl, while their platelet counts ranged from 6.0 to 96.0 x 109/l with a median of 25.5 x 109/l. Lymph nodes were enlarged in 8/15 cases (53.34%), hepatomegly was observed in 4/15 cases (26.67%), splenomegaly in 8/15 cases (53.34%), purpura in 6/15 cases (40%), while pallor was observed in all fifteen cases.Extramedullary leukemia occurred in 4/15 cases (26.67%). As regards the fate of the positive cases, thirteen cases (86.67%) attained complete remission (CR) following induction chemotherapy. Two patients (13.33%) died during induction in active disease. Eight patients were in complete continuous remission (CCR), four patients (26.67%) relapsed and died during relapse, and one patient (6.67%) died in complete remission due to severe neutropenia and infection. On comparing the AML1/ETO fusion gene status with overall survival, no significant difference was found between AML1/ETO positive and negative cases. Likewise, no difference could be found between positive and negative cases as regards disease-free survival (p=0.354). In conclusion, we report a frequency of 19.2% of AML1/ETO fusion gene in our newly diagnosed pediatric AML cases. Positive cases showed good response to induction therapy, as well as high complete remission rates, which are features of good prognosis. Key Words: Pediatric acute myeloid leukemia , AML1/ETO fusion gene , RT-PCR , Clinical outcome , Prognostic significance.