Acute Monocytic Leukemia (French-American-British classification M5) Does Not Have a Worse Prognosis Than Other Subtypes of Acute Myeloid Leukemia: A Report From the Eastern Cooperative Oncology Group

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Abstract
Purpose: Acute monocytic leukemia is a distinct subtype of acute myeloid leukemia (AML) with characteristic biologic and clinical features. This study was designed to compare the outcome of patients with M5 to that of other subtypes of AML, and to identify differences in M5a and M5b. Patients and Methods: We reviewed all patients with AML M5 entered in three clinical trials for newly diagnosed AML conducted by the Eastern Cooperative Oncology Group between 1989 and 1998. Eighty-one patients, 21 with M5a and 60 with M5b, were identified. Results: The complete remission rate was 62% for all patients with M5; 52% for patients with M5a and 65% for patients with M5b (P = .3), and 60% for the 1,122 patients with non-M5 AML entered on the same clinical trials (P = .8 for M5 v non-M5). The 3-year disease-free survival was 26% for all M5 patients; 18% for M5a and 28% for M5b (P = .31), and 33% for non-M5 patients (P = .13 for M5 v non-M5). The 3-year overall survival was 31% for all M5 patients; 33% for M5a and 30% for M5b (P = .65), and 30% for non-M5 (P = .74 for M5 v non-M5). The karyotypes of patients with AML M5 were heterogeneous. CD11b was the only leukemic cell antigen expressed differently in M5a (53%) compared to M5b (77%) to a significant degree (P = .02). Conclusion: AML M5 represents an immunologically heterogeneous population similar to non-M5 AML with a prognosis that is not dependent on morphology. The disease-free survival and overall survival of patients with M5a, M5b, and non-M5 appear not to differ with currently available therapy.