Megakaryoblastic transformation of primary thrombocythemia.

The progression of primary thrombocythemia (PT) into acute leukemia was diagnosed in a 64-year-old man who was previously treated by hydroxyurea without alkylating agents or radioactive phosphorus. Such an event has only been reported in very rare cases. The blast cells had a lymphocytic morphology but were identified as promegakaryoblasts by the ultrastructural demonstration of platelet peroxidase. These data suggest that a megakaryoblastic transformation could occur in PT as had previously been reported in chronic granulocytic leukemia.