Myeloproliferative disorders terminating in acute megakaryoblastic leukemia with chromosome 3q26 abnormality

Two cases of myeloproliferative disorders terminating in acute megakaryoblastic leukemia are reported. One case began as primary myelofibrosis and the other as chronic myelogenous leukemia. Blast cells in the acute leukemic phase were identified as megakaryoblasts by the presence of platelet peroxidase. The clinical course is described, and the morphology, immunologic studies, and ultrastructure studies of the blast cells are reported. On cytogenetic analysis both cases had a translocation involving the No. 3 chromosome locus q26.2. The present data suggest that 3q26 may be associated with transformation of the megakaryocytic lineage.