A 67-year-old female with polycythemia vera who had been followed up for 6 years was admitted to our hospital because of anemia and thrombocytopenia with sudden onset. On CBC, WBC 5,400/μl, RBC 6.25×106/μl, Hb 6.6 g/dl, Hct 20.4%, platelet count 9.9×104/μl. Bone marrow aspiration resulted in dry tap and bone marrow biopsy showed hypoplastic marrow with marked fibrosis. Leukoerythroblastosis on peripheral blood film and extramedullary heamatopoiesis proved by ferrokinetics were also noted. A diagnosis of myelofibrosis was made. About two months later the patient became leukemic and she died of pulmonary infection and hemorrhage. Blast cells were 13∼20μm in diameter and nucleus-cytoplasmic ratio was relatively high. They had none or one nucleoli, basophilic cytoplasma and cytoplasmic bleb. On cytochemistry, myeloperoxidase, Sudan black B and PAS were negative. Acid phosphatase and α-naphtyl butylate esterase were positive. Most of the blast cells were surface GP IIb/IIIa positive and few cells were surface GP Ib positive. Platelet peroxidase reaction on electron microscopy was positive at perinuclear space and endoplasmic reticulum. Blast cells showed differentiation into multinucleated platelet-producing megakaryocytes in in vitro culture. Serum PDGF like activity was increased after leukemic transformation despite of thrombocytopenia and it was thought to be derived from megakaryoblast.
