Multiple myeloma and acute megakaryoblast leukemia in spent phase polycythemia vera. The spontaneous and simultaneous occurrence of multiple myeloma and megakaryoblast leukemia with myelodysplastic features in a case of spent phase polycythemia vera is well documented. In support of the morphologic characteristics of the bone marrow, immunocytologic studies show proliferation of monoclonal plasma cells and megakaryoblasts. The cytogenetic findings of 20q- and unbalanced t(1;7) are consistent with myelodysplastic and leukemic transformation of the bone marrow. These transformations expand observations on variable and spontaneous lineage commitments as the consequence of alterations of the hematopoietic stem cell clone. These data are in support of the changing insights in hematopoiesis as a process of ordered commitment of the stem cell with sequential lineage potentials. 