Acute megakaryocytic leukemia: the Eastern Cooperative Oncology Group experience.

Acute megakaryocytic leukemia (AMegL) is a rare subtype of acute myeloid leukemia (AML) evolving from primitive megakaryoblasts. Because of its rarity and the lack of precise diagnostic criteria in the past, few series of adults treated with contemporary therapy have been reported. Twenty among 1649 (1.2%) patients with newly diagnosed AML entered on Eastern Cooperative Oncology Group (ECOG) trials between 1984 and 1997 were found to have AMegL. The median age was 42.5 years (range 18-70). Marrow fibrosis, usually extensive, was present in the bone marrow. Of the 8 patients who had cytogenetic studies performed, abnormalities of chromosome 3 were the most frequent. The most consistent immunophenotypic finding was absence of myeloperoxidase in blast cells from 5 patients. In the most typical 3 cases, the leukemic cells were positive for one to 2 platelet-specific antigens in addition to lacking myeloperoxidase or an antigen consistent with a lymphoid leukemia. Myeloid antigens other than myeloperoxidase and selected T-cell antigens (CD7 and/or CD2) were frequently expressed. Induction therapy included an anthracycline and cytarabine in all cases. Complete remission (CR) was achieved in 10 of 20 patients (50%). Two patients remain alive, one in CR at 160+ months. Resistant disease was the cause of induction failure in all but 3 patients. The median CR duration was 10.6 months (range 1-160+ months). The median survival for all patients was 10.4 months (range 1-160+ months). Although half of the patients achieved CR, the long-term outcome is extremely poor, primarily attributable to resistant disease. New therapeutic strategies are needed.