[Essential thrombocythemia in transformation to smouldering megakaryoblastic leukemia with myelofibrosis].

Leukemic transformation in essential thrombocythemia (ET) is rare. We describe a patient with ET which transformed to megakaryoblastic leukemia with myelofibrosis after treatment with melphalan for 8 years. His course after transformation smouldered for 20 months without antileukemic chemotherapy. A 61-year-old man was referred by a local doctor to Niigata University Hospital due to nasal bleeding in June 1984. Complete blood count (CBC) was as follows; hemoglobin 12.4 g/dl, platelets 268.8 x 10(4)/microliters, and white blood cells 11,900/microliters, with differentials of 39% PMN, 1% basophils, 2% eosinophils, 4% monocytes, and 13% lymphocytes. Bone marrow examination revealed hyperplasia of megakaryocytes without increase of reticulin fibers. Neutrophil alkaline phosphatase activity and karyotype of marrow cells were normal. ET was diagnosed. He was followed up by local doctor. The platelet count was controlled at a level of approximately 40 x 10(4)/microliters with melphalan for eight years. In January 1992 he developed pain in his lower extremities. He was admitted to our hospital on May 29, 1992. CBC was as follows; hemoglobin 8.9 g/dl, platelets 14.3 x 10(4)/microliters, and white blood cells 3,500/microliters, with differentials of 25% PMN, 5% monocytes, 28% lymphocytes, and 24% blasts. Bone marrow aspiration was unsuccessful and bone marrow biopsy revealed increases in fibroblasts and collagen fibers. Circulating blasts were positive for CD4, CD7, CD25, CD13, CD33, CD34, and HLA-DR and partly positive for CD41 and CD36. In ultrastructural cytochemistry blasts were positive for platelet peroxidase but negative for myeloperoxidase. Cytogenetic study revealed 46, XY, +der (1) t(1:7) (p11;q11) in all of five metaphases. He was diagnosed with megakaryoblastic leukemia accompanied by myelofibrosis.(ABSTRACT TRUNCATED AT 250 WORDS)